Therapy program modification based on a therapy field model

ABSTRACT

Techniques for modeling therapy fields for therapy delivered by medical devices are described. Each therapy field model is based on a set of therapy parameters and represents where therapy will propagate from the therapy system delivering therapy according to the set of therapy parameters. Therapy field models may be useful in guiding the modification of therapy parameters. As one example, a processor compares an algorithmic model of a therapy field to a reference therapy field and adjusts at least one therapy parameter based on the comparison. As another example, a processor adjusts at least one therapy parameter to increase an operating efficiency of the therapy system while substantially maintaining the modeled therapy field.

This application claims the benefit of and is a U.S. National Stagefiling under 35 U.S.C. §371 of PCT Application Serial No.PCT/US09/31650, filed Jan. 22, 2009 and entitled, “THERAPY PROGRAMMODIFICATION BASED ON A THERAPY FIELD MODEL,” which in turn claims thebenefit of U.S. Provisional Application No. 61/048,761, filed Apr. 29,2008 and entitled “THERAPY PROGRAM MODIFICATION BASED ON A THERAPY FIELDMODEL.” The entire disclosure of PCT Application Serial No.PCT/US09/31650 and U.S. Provisional Application No. 61/048,761 isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The disclosure relates to medical devices, and, more particularly,determination of therapy parameter values for therapy delivered bymedical devices.

BACKGROUND

Implantable medical devices, such as electrical stimulators ortherapeutic agent delivery devices, may be used in different therapeuticapplications, such as deep brain stimulation (DBS), spinal cordstimulation (SCS), pelvic stimulation, gastric stimulation, peripheralnerve stimulation or delivery of pharmaceutical agent, insulin, painrelieving agent or anti-inflammatory agent to a target tissue sitewithin a patient. A medical device may be used to deliver therapy to apatient to treat a variety of symptoms or patient conditions such aschronic pain, tremor, Parkinson's disease, other types of movementdisorders, seizure disorders (e.g., epilepsy), urinary or fecalincontinence, sexual dysfunction, obesity, mood disorders, gastroparesisor diabetes. In some cases, the electrical stimulation may be used formuscle stimulation, e.g., functional electrical stimulation (FES) topromote muscle movement or prevent atrophy. In some therapy systems, animplantable electrical stimulator delivers electrical therapy to atarget tissue site within a patient with the aid of one or more medicalleads that include electrodes. In addition to or instead of electricalstimulation therapy, a medical device may deliver a therapeutic agent toa target tissue site within a patient with the aid of one or more fluiddelivery elements, such as a catheter.

During a programming session, which may occur during implant of themedical device, during a trial session, or during a follow-up sessionafter the medical device is implanted in the patient, a clinician mayselect therapy parameter values for the medical device that provideefficacious therapy to the patient. In the case of electricalstimulation, the therapy parameters may include an electrodecombination, and an amplitude, which may be a current or voltageamplitude, a pulse width, and a pulse rate for stimulation signals to bedelivered to the patient. In the case of a therapeutic agent deliverydevice, the therapy parameters may include a dose (e.g., a bolus or agroup of boluses) size, a frequency of bolus delivery, a concentrationof a therapeutic agent in the bolus, a type of therapeutic agent to bedelivered to the patient (if the medical device is configured to delivermore than one type of agent), a lock-out interval, and so forth.

A group of therapy parameter values may be referred to as a therapyprogram. A medical device may deliver therapy to a patient according toone or more stored therapy programs.

SUMMARY

In general, the disclosure is directed toward modifying one or moretherapy parameter values for therapy delivered by a medical device basedon an algorithmic model of a therapy field. The algorithmic model of atherapy field may represent where therapy will propagate from thetherapy system that delivers therapy according to a particular therapyparameter set (or “therapy program”), which defines a value for at leastone therapy parameter.

In one example of modifying one or more therapy parameter values definedby a first therapy program, a therapy field model generated based on thefirst therapy program may be compared to a reference therapy field withknown efficacy for treating a disease or patient condition, or producinga therapeutic outcome. Based on the comparison, one or more therapyparameter values of the first therapy program may be modified togenerate a second therapy program that results in a modified therapyfield that may more closely match the reference field than the therapyfield associated with the first therapy program. An additionalcomparison may be made between the modified therapy field and thereference field to determine if modification to the therapy parametervalues of the second parameter set is desirable.

In some examples, during therapy delivery according to a therapyprogram, a processor may monitor a physiological parameter of a patient,such as by monitoring a signal received from a sensor that generates asignal that changes as a function of the physiological parameter. Theprocessor may detect the occurrence of one or more patient events basedon the signal. The patient event may indicate a change in thetherapeutic efficacy of the therapy program, and may be, for example,the occurrence of a particular symptom related to the patient conditionor a side effect of the therapy delivery. In response to the detectionof a patient event, the processor may analyze the therapy program inview of therapy guidelines that provide information for managing aparticular patient condition. In one example, the therapy guidelines maydefine a reference therapy field, provide a list of functional outcomesfor the therapy delivery, and identify target anatomical structures forthe therapy delivery. The processor may, for example, compare analgorithmic model of a therapy field generated based on therapy deliveryaccording to the therapy program with the reference therapy field inorder to determine whether to modify the therapy program.

In one example, upon detecting the patient event, the processor mayselect a different set of therapy guidelines and generate anothertherapy program based on the new set of therapy guidelines in order togenerate a different therapy field (e.g., a stimulation field) that maybetter address the patient condition. As another example, the processormay use the same set of therapy guidelines but increase the strength ofthe therapy delivery (e.g., increase the stimulation) to increase thesize of the therapy field. In either example, the processor may adjust avalue of one or more therapy parameters based on the analysis of thetherapy parameter set in view of one or more sets of therapy guidelines.

In another example of modifying a therapy program based on analgorithmic model of a therapy field, one or more of the therapyparameter values of the therapy program may be adjusted to increase anoperating efficiency of the therapy system while substantiallymaintaining the therapy field that results from therapy delivery basedon the therapy program. Substantially maintaining the therapy field maybe desirable if the therapy field is known to provide efficacioustherapy for the patient, which may be indicated by therapeutic resultswith minimal side effects. The operating efficiency of the therapysystem may be increased, for example, by decreasing power consumption oroperating at efficient amplitudes based on voltage multiplier levels. Insome examples, an algorithmic model of the therapy field may begenerated based on the adjusted parameter values and compared to theoriginal modeled therapy field. If the difference between one or morefield characteristics of the therapy field model generated according tothe adjusted parameters and the original therapy field model are below athreshold, a processor of the therapy system may determine that thetherapy field is substantially maintained.

In one example, the disclosure describes a method comprising determininga first therapy program that comprises a set of therapy parametervalues, generating an algorithmic model of a therapy field based on thefirst therapy program, wherein the algorithmic model of the therapyfield represents where therapy will propagate from a therapy systemdelivering the therapy according to the first therapy program,determining therapy guidelines based on a patient condition, wherein thetherapy guidelines comprise a reference therapy field, comparing thealgorithmic model of the first therapy field to the reference therapyfield, and adjusting a value of at least one of the therapy parametersof the first therapy program to generate a second therapy program basedon the comparison.

In another example, the disclosure describes a system comprising atherapy system that delivers a therapy to a patient according to a firsttherapy program comprising a set of therapy parameter values and aprocessor that generates an algorithmic model of a therapy field basedon the therapy program, the model representing where the therapy willpropagate from the therapy system when the medical device deliverstherapy according to the first therapy program, determines therapyguidelines based on a patient condition, wherein the therapy guidelinescomprise a reference therapy field, compares the algorithmic model ofthe therapy field to the reference therapy field, and, based on thecomparison, adjusts a value of at least one of the therapy parameters ofthe first therapy program to generate a second therapy program.

In another example, the disclosure describes a therapy system comprisingmeans for determining a first therapy program that comprises a set oftherapy parameter values, means for delivering a therapy to a targettherapy site in a patient according to the first therapy program, andmeans for generating an algorithmic model of a therapy field based onthe first therapy program, the model representing where the therapy willpropagate from the means for delivering, determining therapy guidelinesbased on a patient condition, wherein the therapy guidelines comprise areference therapy field, comparing the algorithmic model of the therapyfield to the reference therapy field, and adjusting a value of at leastone therapy parameter of the first therapy program to generate a secondtherapy program based on the comparison.

In another example, the disclosure describes a method comprisingdelivering therapy to a patient via a therapy system according to atherapy program, generating an algorithmic model of a therapy fieldbased on the therapy program, wherein the algorithmic model of thetherapy field represents where therapy will propagate from the therapysystem delivering the therapy according to the therapy program,detecting a patient event, upon detecting the patient event, referencingtherapy guidelines that comprise a reference therapy field, comparingthe algorithmic model of the therapy field to the reference therapyfield, and adjusting a value of at least one therapy parameter of thetherapy program based on the comparison between the algorithmic model ofthe therapy field and the reference therapy field.

In another example, the disclosure describes a method comprisingdetermining a first therapy program that comprises a set of therapyparameters values, generating an algorithmic model of a therapy fieldbased on the first therapy program, the algorithmic model representingwhere therapy will propagate from the therapy system delivering therapyaccording to the first therapy program, and automatically determining asecond therapy program that increases an operating efficiency of thetherapy system while substantially maintaining the therapy field.

In another example, the disclosure describes a therapy system comprisinga medical device that delivers a therapy to a patient according to afirst therapy program that comprises a first set of therapy parametersand a processor that generates an algorithmic model of a therapy fieldbased on the first therapy program, wherein the model represents wherethe therapy will propagate from the medical device delivering therapyaccording to the first therapy program, and automatically determines asecond therapy program that increases an operating efficiency of thetherapy system while substantially maintaining the therapy field.

In yet another example, the disclosure describes a system comprisingmeans for determining a therapy program that comprises a first set oftherapy parameters values, means for delivering a therapy to a targettherapy site in a patient according to the therapy program, and meansfor generating an algorithmic model of a therapy field based on thetherapy program, wherein the model represents where the therapy willpropagate from the means for delivery and automatically determining asecond set of therapy parameters that increase an operating efficiencyof the therapy system while substantially maintaining the therapy field.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are conceptual diagrams illustrating example therapysystems that provide electrical stimulation therapy to a patient.

FIG. 2 is a functional block diagram of an example implantable medicaldevice that generates electrical stimulation signals.

FIG. 3 is a functional block diagram of an example medical deviceprogrammer.

FIGS. 4A-4C are flow diagrams illustrating example techniques formodifying therapy parameters based on an algorithmic model of a therapyfield.

FIG. 5 is a flow diagram illustrating another example technique formodifying therapy parameters based on an algorithmic model of a therapyfield.

FIG. 6A illustrates a schematic representation of an example graphicaluser interface (GUI) that displays therapy categories via the display ofthe programmer of FIG. 3.

FIG. 6B illustrates a schematic representation of an example GUI thatdisplays a listing of patient conditions within a therapy category viathe display of the programmer of FIG. 3.

FIG. 6C illustrates a schematic representation of an example GUI thatdisplays therapy guidelines for a selected patient condition via thedisplay of the programmer of FIG. 3.

FIG. 7 illustrates a schematic representation of an example GUI that maybe presented on the display of the user interface of the programmer ofFIG. 3.

FIG. 8 illustrates an example GUI that displays a stimulation field viewto the user via the display of the programmer of FIG. 3.

FIG. 9 illustrates an example GUI that displays an activation field viewto the user via the display of the programmer of FIG. 3.

FIG. 10 is a flow diagram illustrating an example technique forcalculating and displaying an electrical field model, which is based ona stimulation field.

FIG. 11 is a flow diagram illustrating an example technique forcalculating and displaying the activation field model of definedstimulation.

FIG. 12 is a schematic illustration of another example of a GUI that maybe presented on the display of the programmer of FIG. 3 in order to helpa user generate an algorithmic model of a therapy field.

FIG. 13 is a flow diagram illustrating an example technique foradjusting stimulation parameters.

FIG. 14 is an example screen shot of a GUI that presents a sagittal viewof a patient anatomy with an algorithmic model of an electrical field.

FIG. 15 is a conceptual diagram illustrating a three-dimensional (3D)visualization environment including a 3D brain model for defining a 3Dstimulation field.

FIG. 16 is a flow diagram illustrating an example technique for defininga 3D stimulation field within a 3D brain model.

DETAILED DESCRIPTION

In general, the disclosure is directed toward modifying one or moretherapy parameter values for therapy delivered by a medical device basedon an algorithmic model of a therapy field. An algorithmic model of atherapy field may be generated based on a therapy parameter set thatdefines a value for at least one therapy parameter, and represents wheretherapy will propagate from the therapy system delivering therapyaccording to the therapy parameter set.

FIG. 1A is a conceptual diagram illustrating an example therapy system10 that provides electrical stimulation therapy to patient 12. Therapysystem 10 includes IMD 14 and medical lead 16. In the example shown inFIG. 1A, IMD 14 provides deep brain stimulation (DBS) to brain 18 ofpatient 12. Lead 16 is implanted within patient 12 such that one or moreelectrodes 17 carried by lead 16 are located proximate to a targettissue site within brain 18. IMD 14 provides electrical stimulation toregions within brain 18 in order to manage a condition of patient 12,such as to mitigate the severity or duration of the patient condition.In some examples, more than one lead 16 may be implanted within brain 18of patient 12 to provide stimulation to multiple anatomical regions ofbrain 18. As shown in FIG. 1A, system 10 may also include a programmer20, which may be a handheld device, portable computer, or workstationthat provides a user interface to a clinician or other user. Theclinician may interact with the user interface to program stimulationparameters for IMD 14.

DBS may be used to treat various patient conditions, such as, but notlimited to, seizure disorders (e.g., epilepsy), pain, migraineheadaches, psychiatric disorders (e.g., obsessive compulsive disorder,mood disorders or anxiety disorders), movement disorders (e.g.,essential tremor or Parkinson's disease), Huntington's disease, andother neurodegenerative disorders. The anatomic region within patient 12that serve as the target tissue site for stimulation delivered by IMD 14may be selected based on the patient condition. For example, stimulatingan anatomical region, such as the Substantia Nigra, in brain 18 mayreduce the number and magnitude of tremors experienced by patient 12.Other example target anatomical regions for treatment of movementdisorders may include the subthalamic nucleus, globus pallidus interna,ventral intermediate, and zona inserta. Anatomical regions such as thesemay be targeted by the clinician during implantation of lead 16. Inother words, the clinician may attempts to position lead 16 within orproximate to these target regions within brain 18.

While DBS may successfully reduce symptoms of some neurologicaldiseases, the stimulation may cause unwanted side effects as well. Sideeffects may include incontinence, tingling, loss of balance, paralysis,slurred speech, loss of memory, and many other neurological issues. Sideeffects may be mild to severe; however, most side effects are reversiblewhen stimulation is stopped. DBS may cause one or more side effects byinadvertently providing electrical stimulation to anatomical regionsnear the targeted anatomical region. For this reason, the clinician mayprogram the stimulation parameters in order to balance effective therapyand minimal side effects.

DBS lead 16 may include one or more electrodes 17 placed along thelongitudinal axis of lead 16. In some examples, electrodes 17 mayinclude at least one ring electrode that resides along the entirecircumference of lead 16. Electrical current from the ring electrodespropagates in all directions from the active electrode. The resultingstimulation field reaches anatomical regions of brain 18 within acertain distance in all directions. The stimulation field may reach thetarget anatomical region, but the stimulation field may also affectnon-target anatomical regions and produce unwanted side effects. Inother examples, lead 16 may include a complex electrode array geometrythat includes segmented or partial ring electrodes in addition to orinstead of ring electrodes. The electrodes in a complex electrode arraymay be located at different axial and angular positions around thecircumference of the lead, as well as at different longitudinalpositions (i.e., along the longitudinal axis of lead 16). A complexelectrode array geometry may be useful for customizing the stimulationfield and provide improved therapy while decreasing side effects. Forexample, with a complex electrode array, electrodes may be selectedalong the longitudinal axis of lead 16 as well as along thecircumference of lead 16. Activating selective electrodes of lead 16 canproduce customizable stimulation fields that may be directed to aparticular side of lead 16 in order to isolate the stimulation fieldaround the target anatomical region of brain 18. In this manner,specific electrodes of the complex electrode array geometry may beselected to produce a stimulation field at desired portions of thecircumference instead of always producing a stimulation field around theentire circumference of the lead, as with some ring electrodes.

Producing irregular stimulation fields with a lead 16 with a complexelectrode geometry may allow therapy system 10 to more effectively treatcertain anatomical regions of brain 18. In some cases, a therapy system10 including lead 16 with a complex electrode array may also help reduceor eliminate side effects from more spherical stimulation fieldsproduced by a conventional array of ring electrodes. The center of thestimulation field may be moved away from lead 16 to avoid unwantedstimulation or compensate for inaccurately placed leads.

In the example shown in FIG. 1A, lead 16 is coupled to IMD 14 viaconnector 22, which defines a plurality of electrical contacts forelectrically coupling electrodes 17 to a stimulation generator withinIMD 14. Connector 22 may also be referred to as a connector block orheader of IMD 14. Lead 16 is indirectly coupled to connector 22 with theaid of lead extension 24. In some examples, lead 16 may be directlycoupled to connector 22 without the aid of extension 24.

Programmer 20 is an external computing device that is configured towirelessly communicate with IMD 14. For example, programmer 20 may be aclinician programmer that the clinician uses to communicate with IMD 14.Alternatively, programmer 20 may be a patient programmer that allowspatient 12 to view and modify therapy parameters. The clinicianprogrammer may include more programming features than the patientprogrammer. In other words, more complex or sensitive tasks may only beallowed by the clinician programmer to prevent patient 12 from makingundesired changes to IMD 14.

Programmer 20 may be a hand-held computing device that includes adisplay viewable by the user and a user input mechanism that can be usedto provide input to programmer 20. For example, programmer 20 mayinclude a small display screen (e.g., a liquid crystal display or alight emitting diode display) that presents information to the user. Inaddition, programmer 20 may include a keypad, buttons, a peripheralpointing device, touch screen or another input mechanism that allows theuser to navigate though the user interface of programmer 20 and provideinput.

If programmer 20 includes buttons and a keypad, the buttons may bededicated to performing a certain function, i.e., a power button, or thebuttons and the keypad may be soft keys that change in functiondepending upon the section of the user interface currently viewed by theuser. Alternatively, the screen (not shown) of programmer 20 may be atouch screen that allows the user to provide input directly to the userinterface shown on the display. The user may use a stylus or theirfinger to provide input to the display.

In other examples, rather than being a handheld computing device or adedicated computing device, programmer 20 may be a larger workstation ora separate application within another multi-function device. Forexample, the multi-function device may be a cellular phone or personaldigital assistant that can be configured to an application to simulateprogrammer 20. Alternatively, a notebook computer, tablet computer, orother personal computer may enter an application to become programmer 20with a wireless adapter connected to the personal computer forcommunicating with IMD 14.

When programmer 20 is configured for use by the clinician, programmer 20may be used to transmit initial programming information to IMD 14. Thisinitial information may include system 10 hardware information such asthe type of lead 16, the position of lead 16 within patient 12, thetherapy parameter values of therapy programs stored within IMD 14 orwithin programmer 20, and any other information the clinician desires toprogram into IMD 14.

With the aid of programmer 20 or another computing device, a clinicianmay select values for therapy parameters for controlling therapydelivery by therapy system 10. The values for the therapy parameters maybe organized into a group of parameter values referred to as a “therapyprogram” or “therapy parameter set.” “Therapy program” and “therapyparameter set” are used interchangeably herein. In the case ofelectrical stimulation, the therapy parameters may include an electrodecombination, and an amplitude, which may be a current or voltageamplitude, and, if IMD 14 delivers electrical pulses, a pulse width, anda pulse rate for stimulation signals to be delivered to the patient.Other example therapy parameters include a slew rate, duty cycle, andphase of the electrical stimulation signal. An electrode combination mayinclude a selected subset of one or more electrodes 17 located on one ormore implantable lead 16 coupled to IMD 14. The electrode combinationmay also refer to the polarities of the electrodes in the selectedsubset. By selecting particular electrode combinations, a clinician maytarget particular anatomic structures within brain 18 of patient 12. Inaddition, by selecting values for slow rate, duty cycle, phaseamplitude, pulse width, and/or pulse rate, the physician can attempt togenerate an efficacious therapy for patient 12 that is delivered via theselected electrode subset. Due to physiological diversity, conditiondifferences, and inaccuracies in lead placement, the parameters maygreatly vary between patients.

During a programming session, the clinician may determine one or moretherapy programs that may provide effective therapy to patient 12.Patient 12 may provide feedback to the clinician as to the efficacy ofthe specific program being evaluated. Once the clinician has identifiedone or more programs that may be beneficial to patient 12, patient 12may continue the evaluation process and determine which program bestalleviates the condition of patient 12 or otherwise provides efficacioustherapy to patient 12. Programmer 20 may assist the clinician in thecreation/identification of therapy programs by providing a methodicalsystem of identifying potentially beneficial therapy parameters.

In some examples, the clinician may select therapy parameters using thetechniques described in commonly-assigned U.S. Pat. No. 7,822,483 issuedon Oct. 26, 2010 to Stone et al., entitled, “ELECTRICAL AND ACTIVATIONFIELD MODELS FOR CONFIGURING STIMULATION THERAPY” and filed on Oct. 31,2006, and commonly-assigned U.S. Patent Application Publication No.2007/0203541 by Goetz et al., entitled, “PROGRAMMING INTERFACE WITH ACROSS-SECTIONAL VIEW OF A STIMULATION LEAD WITH COMPLEX ELECTRODE ARRAYGEOMETRY,” and filed on Oct. 31, 2006. U.S. Pat. No. 7,822,483 and U.S.Patent Application Publication No. 2007/0203541 describe programmingsystems and methods that support the programming of stimulationparameters with a therapy system 10 including a lead 16, which mayinclude a complex electrode array geometry.

In accordance with techniques described in U.S. Pat. No. 7,822,483 toStone et al., a user interface of programmer 20 may display arepresentation of the anatomical regions of patient 12, such asanatomical regions of brain 18. The three-dimensional (3D) space of theanatomical regions may be displayed as multiple two-dimensional (2D)views or a 3D visualization environment. Lead 16 may also be representedon the display of the user interface, positioned according to the actualimplantation location by the clinician or directly from an image takenof the lead within brain 18. The clinician may interact with the userinterface of programmer 20 to manually select and program certainelectrodes of lead 16, select an electrode level of the lead and adjustthe resulting stimulation field with the anatomical regions as guides,or defining one or more stimulation fields that only affect anatomicalregions of interest. Once the clinician has defined the one or morestimulation fields, system 10 automatically generates the stimulationparameter values associated with each of the stimulation fields andtransmits the parameter values to IMD 14. The stimulation parametervalues may be stored as therapy programs within a memory of IMD 14and/or a memory within programmer 20.

In accordance with techniques described in U.S. Patent Publication No.2007/0203541 by Goetz et al., programmer 20 may present a user interfacethat displays electrodes 17 of lead 16 and enables a user to selectindividual electrodes to form an electrode combination and specifyparameters for stimulation delivered via the selected electrodecombination. In accordance with other techniques described in U.S.Patent Publication No. 2007/0203541 by Goetz et al., programmer 20 maypresent a user interface to a user that enables the user to manipulate arepresentation of an electrical stimulation field (i.e., one type oftherapy field) produced by a selected electrode combination. A processorwithin programmer 20 may then select the appropriate electrodecombination, electrode polarities, amplitudes, pulse widths, and pulserates of electrical stimulation sufficient to support the fieldmanipulation operations inputted by the user into programmer 20. Thatis, programmer 20 may automatically generate a therapy program that bestfits a stimulation field created by a user via a user interface ofprogrammer 20.

Programmer 20 may also be configured for use by patient 12. Whenconfigured as the patient programmer, programmer 20 may have limitedfunctionality in order to prevent patient 12 from altering criticalfunctions or applications that may be harmful to patient 12. In thismanner, programmer 20 may only allow patient 12 to adjust certaintherapy parameters or set an available range of values for a particulartherapy parameter. Programmer 20 may also provide an indication topatient 12 when therapy is being delivered or when IMD 14 or when thepower source within programmer 20 or IMD 14 need to be replaced orrecharged.

Whether programmer 20 is configured for clinician or patient use,programmer 20 may communicate with IMD 14 or any other computing devicevia wireless communication. Programmer 20, for example, may communicatevia wireless communication with IMD 14 using radio frequency (RF)telemetry techniques known in the art. Programmer 20 may alsocommunicate with another programmer or computing device via a wired orwireless connection using any of a variety of local wirelesscommunication techniques, such as RF communication according to the802.11 or Bluetooth specification sets, infrared communication accordingto the IRDA specification set, or other standard or proprietarytelemetry protocols. Programmer 20 may also communicate with anotherprogramming or computing device via exchange of removable media, such asmagnetic or optical disks, or memory cards or sticks. Further,programmer 20 may communicate with IMD 14 and other another programmervia remote telemetry techniques known in the art, communicating via alocal area network (LAN), wide area network (WAN), public switchedtelephone network (PSTN), or cellular telephone network, for example.

In other applications of therapy system 10, the target therapy deliverysite within patient 12 may be a location proximate to a spinal cord orsacral nerves (e.g., the S2, S3 or S4 sacral nerves) in patient 12 orany other suitable nerve, organ, muscle or muscle group in patient 12,which may be selected based on, for example, a patient condition. Forexample, therapy system 10 may be used to deliver an electricalstimulation to tissue proximate to a pudendal nerve, a perineal nerve orother areas of the nervous system, in which cases, lead 16 would beimplanted and substantially fixed proximate to the respective nerve. Asfurther examples, an electrical stimulation system may be positioned todeliver a stimulation to help manage peripheral neuropathy orpost-operative pain mitigation, ilioinguinal nerve stimulation,intercostal nerve stimulation, gastric stimulation for the treatment ofgastric mobility disorders and obesity, muscle stimulation, formitigation of other peripheral and localized pain (e.g., leg pain orback pain). In addition, although a single lead 16 is shown in FIG. 1A,in some therapy systems, two or more leads may be electrically coupledto IMD 14.

FIG. 1B is a conceptual diagram of another example of therapy system 30that delivers electrical stimulation to target tissue sites proximate tospine 32 of patient 12. Therapy system 30 includes IMD 14, which iscoupled to leads 34, 36 via connector 22. Leads 34, 36 each include anarray of electrodes 35, 37, respectively. IMD 14 may deliver stimulationto patient 12 via a combination of electrodes 35, 37. Electrodes 35, 37may each be any suitable type of electrode, such as a ring electrode,partial ring electrode or segmented electrode.

In some examples, the array of electrodes 35, 37, as well as electrodes17 of therapy system 10 (FIG. 1A), may also include at least one senseelectrode that senses a physiological parameter of patient 12, such as,but not limited to, a heart rate, respiration rate, respiratory volume,core temperature, muscular activity, electromyogram (EMG), anelectroencephalogram (EEG), an electrocardiogram (ECG) or galvanic skinresponse. Therapy systems 10, 30 may also include sensor 26 (shown inFIG. 1A) in addition to or instead of sense electrodes on the leads 16,34, 36. Sensor 26 may be a sensor configured to detect an activitylevel, posture, or another physiological parameter of patient 12. Forexample, sensor 26 may generate a signal that changes as a function ofthe physiological parameter of patient 12. Sensor 26 may be implanted orexternal to patient 12, and may be wirelessly coupled to IMD 14 or via alead, such as leads 16, 34, 36, or another lead. For example, sensor 26may be implanted within patient 12 at a different site than IMD 14 orsensor 26 may be external to patient 12. In some examples, sensor 26 maybe incorporated into a common housing with IMD 14. In addition orinstead of being coupled to IMD 14, in some cases, sensor 26 may bewirelessly coupled to programmer 20 or coupled to programmer 20 by awired connection.

In the example shown in FIG. 1B, leads 34, 36 are positioned to deliverbilateral stimulation to patient 12, i.e., stimulation signals aredelivered to target tissue sites on opposite sides of a midline ofpatient 12. The midline may generally be defined along spinal cord 32.Just as with therapy system 10, a clinician may generate one or moretherapy programs for therapy system 30 by selecting values for one ormore types of therapy parameters that provide efficacious therapy topatient 12 with the aid of programmer 20 or another computing device.The therapy parameters may include, for example, a combination of theelectrodes of leads 34 and/or 36, the voltage or current amplitude,pulse width, and frequency of stimulation.

For therapy system 10 (FIG. 1A), therapy system 30 (FIG. 1B) or anyother therapy system that provides therapy to patient 12, an algorithmicmodel of a therapy field (also referred to as a “therapy field model”)may be generated with the aid of modeling software, hardware or firmwareexecuting on a computing device, such as programmer 20 or a separatededicated or multifunction computing device. The therapy field model maybe based on a therapy program defining respective values for one or moretherapy parameters and may represent where therapy will propagate from atherapy system (e.g., leads 16, 34 or 36) delivering therapy accordingto the therapy program. The therapy field model may be useful forguiding the modification of the therapy parameter values of the therapyprogram. For example, the therapy field model may be compared to areference therapy field and one or more of the therapy parameter valuesdefined by the therapy program may be modified based on the comparison.Additionally or alternatively, the therapy field model may be used toadjust therapy parameter values to increase an operating efficiency ofthe therapy system while substantially maintaining at least one fieldcharacteristic of the therapy field model.

The therapy field model may be stored within a memory of programmer 20,IMD 14 or another device. While the remainder of the description ofFIGS. 2-5 primarily refers to therapy system 30 of FIG. 1B, in otherexamples, the techniques for generating an algorithmic model of atherapy field may be applied to therapy system 10 of FIG. 1A thatprovides DBS to patient 12. In addition, while the remainder of thedescription primarily refers to an algorithmic model of a therapy fieldthat is generated with the aid of modeling software executing on acomputing device, in other examples, the algorithmic model of a therapyfield may be generated with the aid of hardware or firmware in additionto or instead of software.

In some examples, the modeling software implements an algorithm thatmodels the therapy field based on a therapy program, an anatomy ofpatient 12, and the hardware characteristics of therapy system 10 ortherapy system 30. In the case of therapy system 30 (FIG. 1B), thehardware characteristics may include the type of IMD 14, which mayinclude the energy threshold for the particular type of IMD 14, the typeof leads 34, 36, which may include the type of electrodes 35, 37 (e.g.,ring electrodes, partial ring electrodes or segmented electrodes), and abaseline impedance presented to IMD 14 at the time of programming, i.e.,the impedance of the entire path between IMD 14 and the target tissuesite, including the lead conductors, electrodes 35, 37, and patienttissue through which stimulation propagates. In examples in which atherapy system includes two or more leads 34, 36, the hardwarecharacteristics of therapy system 30 may include a baseline distancebetween the electrodes 35, 37 of the respective leads 34, 36. Thebaseline spacing between electrodes 35, 37 of leads 34, 36 may be, forexample, the spacing between electrodes 35, 37 at the time of implant ofleads 34, 36. The algorithm for generating the therapy field model maybe stored within a memory of programmer 20, IMD 14 or another device.

In examples in which a clinician generates therapy programs for IMD 14by selecting a stimulation field and subsequently generating thestimulation parameter values that may achieve the stimulation field, thetherapy field may be an algorithmic model of the stimulation fieldselected by the clinician. For example, the therapy field may be anelectrical field model that is generated based upon a patient anatomydata and a therapy program defining stimulation parameter values, wherethe electrical field model represents the areas of a patient anatomicalregion that will be covered by an electrical field during therapydelivery. The patient anatomy data may be specific to patient 12 or mayrepresent data for more than one patient, e.g., model or averaged dataof the anatomical structure and tissue conductivity of multiplepatients. With respect to therapy system 30 of FIG. 1B, the electricalfield model represents where electrical stimulation propagates throughtissue from electrodes 35, 37 of leads 34, 36. Patient anatomy data mayindicate one or more characteristics of patient tissue (e.g., impedance)proximate to implanted leads 34, 36, and may be created from any type ofimaging modality, such as, but not limited to, computed tomography (CT),magnetic resonance imaging (MRI), x-ray, fluoroscopy, and the like.

In other examples, the therapy field may be an activation field modelthat may be based on a neuron model that indicates one or morecharacteristics of patient neural tissue proximate to electrodes 35, 37of implanted leads 34, 36, respectively. The activation field mayindicate the neurons that will be activated by the electrical field inthe anatomical region. The clinician may program the therapy parametervalues for one or more therapy programs for guiding the therapy deliveryby IMD 14 by selecting a desired therapy field and generating therapyparameter values that may achieve the desired therapy field, taking intoconsideration the patient's anatomy and the hardware characteristics oftherapy system 30. As previously indicated, the hardware characteristicsmay include the type of IMD 14, the type of leads 34, 36, the type ofelectrodes 35, 37, and the spacing between the leads 34, 36 and/orelectrodes 35, 37 within patient 12.

In other examples, an algorithmic model of the therapy field may begenerated after selecting a therapy program. For example, the clinicianmay select therapy parameter values that provide efficacious therapy topatient 12 and generate the therapy field resulting from the therapyparameter values with the aid of modeling software executing on acomputing device, such as programmer 20 or a separate workstation orcomputing device. Again, the resulting therapy field may be based on analgorithmic model that takes into consideration the therapy parametervalues of the therapy program, the patient's anatomy, and the hardwarecharacteristics of therapy system 30.

FIG. 2 is a functional block diagram of an example IMD 14. IMD 14includes a processor 40, memory 42, stimulation generator 44, switchingmodule 46, telemetry module 48, and power source 50. As shown in FIG. 2,stimulation generator 44 is coupled to leads 34, 36. Alternatively,stimulation generator 44 may be coupled to a single lead (e.g., as shownin FIG. 1A) or more than three leads directly or indirectly (e.g., via alead extension, such as a bifurcating lead extension that mayelectrically and mechanically couple to two leads) as needed to providestimulation therapy to patient 12.

In the example illustrated in FIG. 2, lead 34 includes electrodes35A-35D (collectively referred to as “electrodes 35”) and lead 36includes electrodes 37A-37D (collectively referred to as “electrodes37”). Electrodes 35, 37 may be ring electrodes. In other examples,electrodes 35, 37 may be arranged in a complex electrode array thatincludes multiple non-contiguous electrodes at different angularpositions about the outer circumference of the respective lead 34, 36,as well as different levels of electrodes spaced along a longitudinalaxis of the respective lead 34, 36. The configuration, type, and numberof electrodes 35, 37 illustrated in FIG. 2 are merely exemplary. Inother examples, IMD 14 may be coupled to any suitable number of leadswith any suitable number and configuration of electrodes.

Memory 42 includes computer-readable instructions that, when executed byprocessor 40, cause IMD 14 to perform various functions. Memory 42 mayinclude any volatile, non-volatile, magnetic, optical, or electricalmedia, such as a random access memory (RAM), read-only memory (ROM),non-volatile RAM (NVRAM), electrically-erasable programmable ROM(EEPROM), flash memory, or any other digital media. Memory 42 mayinclude programs 52, program groups 54, and operating instructions 56 inseparate memories within memory 42 or separate areas within memory 42.Each program 52 defines a particular program of therapy in terms ofrespective values for electrical stimulation parameters, such aselectrode combination, electrode polarity, current or voltage amplitude,pulse width and pulse rate. A program group 54 defines a group ofprograms that may be delivered together on an overlapping ornon-overlapping basis. Operating instructions 56 guide general operationof IMD 14 under control of processor 40, and may include instructionsfor measuring the impedance of electrodes 35, 37 and/or determining thedistance between electrodes 35, 37.

Stimulation generator 44 produces stimulation signals, which may bepulses as primarily described herein, or continuous time signals, suchas sine waves, for delivery to patient 12 via selected combinations ofelectrodes 35, 37. Processor 40 controls stimulation generator 44according to programs 52 and program groups 54 stored by memory 42 toapply particular stimulation parameter values specified by one or moreof programs, such as amplitude, pulse width, and pulse rate. Processor40 may include any one or more microprocessors, controllers, digitalsignal processors (DSPs), application specific integrated circuits(ASICs), field-programmable gate arrays (FPGAs), or equivalent discreteor integrated digital or analog logic circuitry, and the functionsattributed to processor 40 herein may be embodied as software, firmware,hardware or any combination thereof.

Processor 40 also controls switching module 46 to apply the stimulationsignals generated by stimulation generator 44 to selected combinationsof electrodes 35, 37. In particular, switching module 46 couplesstimulation signals to selected conductors within leads 34, 36 which, inturn, deliver the stimulation signals across selected electrodes 35, 37.Switching module 46 may be a switch array, switch matrix, multiplexer,or any other type of switching device suitable to selectively couplestimulation energy to selected electrodes. Hence, stimulation generator44 is coupled to electrodes 35, 37 via switching module 46 andconductors within leads 34, 36. In some examples, IMD 14 does notinclude switching module 46.

Stimulation generator 44 may be a single or multi-channel stimulationgenerator. In particular, stimulation generator 44 may be capable ofdelivering, a single stimulation pulse, multiple stimulation pulses, ora continuous signal at a given time via a single electrode combinationor multiple stimulation pulses at a given time via multiple electrodecombinations. In some examples, however, stimulation generator 44 andswitching module 46 may be configured to deliver multiple channels on atime-interleaved basis. In this case, switching module 46 serves to timedivision multiplex the output of stimulation generator 44 acrossdifferent electrode combinations at different times to deliver multipleprograms or channels of stimulation energy to patient 12.

Telemetry module 48 supports wireless communication between IMD 14 andan external programmer 20 or another computing device under the controlof processor 40. Processor 40 of IMD 14 may receive, as updates toprograms, values for various stimulation parameters such as amplitudeand electrode combination, from programmer 20 via telemetry interface48. The updates to the therapy programs may be stored within programs 52portion of memory 42.

The various components of IMD 14 are coupled to power supply 50, whichmay include a rechargeable or non-rechargeable battery. Anon-rechargeable battery may be selected to last for several years,while a rechargeable battery may be inductively charged from an externaldevice, e.g., on a daily or weekly basis. In other examples, powersupply 50 may be powered by proximal inductive interaction with anexternal power supply carried by patient 12.

FIG. 3 is a functional block diagram of an example of programmer 20. Asshown in FIG. 3, external programmer 20 includes processor 60, memory62, user interface 64, telemetry module 66, and power source 68. Aclinician or another user may interact with programmer 20 to generateand/or select therapy programs for delivery in IMD 14. For example, insome examples, programmer 20 may allow a clinician to define stimulationfields and generate appropriate stimulation parameter values. Programmer20 may be used to present anatomical regions to the user via userinterface 64, select therapy programs, generate new therapy programs bymanipulating stimulation fields, and transmit the new therapy programsto IMD 14, as described in U.S. Pat. No. 7,822,483 issued on Oct. 26,2010 to Stone et al. and entitled, “ELECTRICAL AND ACTIVATION FIELDMODELS FOR CONFIGURING STIMULATION THERAPY.” Processor 60 may storestimulation parameter values as one or more therapy programs in memory62. Processor 60 may send programs to IMD 14 via telemetry module 66 tocontrol stimulation automatically and/or as directed by the user.

As previously described, programmer 20 may be a handheld computingdevice, a workstation or another dedicated or multifunction computingdevice. For example, programmer 20 may be a general purpose computingdevice (e.g., a personal computer, personal digital assistant (PDA),cell phone, and so forth) or may be a computing device dedicated toprogramming IMD 14. Programmer 20 may be one of a clinician programmeror a patient programmer in some examples, i.e., the programmer may beconfigured for use depending on the intended user. A clinicianprogrammer may include more functionality than the patient programmer.For example, a clinician programmer may include a more featured userinterface that allows a clinician to download usage and statusinformation from IMD 14, and allows the clinician to control aspects ofIMD 14 not accessible by a patient programmer example of programmer 20.

A user, either a clinician or patient 12, may interact with processor 60through user interface 64. User interface 64 may include a display, suchas a liquid crystal display (LCD), light-emitting diode (LED) display,or other screen, to present information related to stimulation therapy,and buttons or a pad to provide input to programmer 20. In exampleswhere user interface 64 requires a 3D environment, the user interfacemay support 3D environments such as a holographic display, astereoscopic display, an autostereoscopic display, a head-mounted 3Ddisplay, or any other display that is capable of presenting a 3D imageto the user. Buttons of user interface 64 may include an on/off switch,plus and minus buttons to zoom in or out or navigate through options, aselect button to pick or store an input, and pointing device, e.g. amouse, trackball, or stylus. Other input devices may be a wheel toscroll through options or a touch pad to move a pointing device on thedisplay. In some examples, the display may be a touch screen thatenables the user to select options directly from the display screen.

Processor 60 processes instructions from memory 62 and may store userinput received through user interface 64 into the memory whenappropriate for the current therapy. In addition, processor 60 providesand supports any of the functionality described herein with respect toeach example of user interface 64. Processor 60 may comprise any one ormore of a microprocessor, DSP, ASIC, FPGA, or other digital logiccircuitry, and the functions attributed to processor 60 herein may beembodied as software, firmware, hardware or any combination thereof.

Memory 62 may include any one or more of a RAM, ROM, EEPROM, flashmemory, or the like. Memory 62 may include instructions for operatinguser interface 64, telemetry module 66, and managing power source 68.Memory 62 may store program instructions that, when executed byprocessor 60, cause the processor and programmer 20 to provide thefunctionality ascribed to them herein. Memory 62 also includesinstructions for generating therapy programs, such as instructions fordetermining stimulation parameters for achieving a user-selectedstimulation fields or instructions for determining a resultingstimulation field from user-selected stimulation parameters. Memory 62may also include a removable memory portion that may be used to providememory updates or increases in memory capacities. A removable memory mayalso allow patient data to be easily transferred to another computingdevice, or to be removed before programmer 20 is used to program therapyfor another patient.

Programmer 20 may communicate wirelessly with IMD 14 or another device,such as using RF communication or proximal inductive interaction. Thiswireless communication is possible through the use of telemetry module66, which may be coupled to an internal antenna or an external antenna.An external antenna that is coupled to programmer 24 may correspond tothe programming head that may be placed over the patient's skin near theimplanted IMD 14.

Telemetry module 66 may also be configured to communicate with anothercomputing device via wireless communication techniques, or directcommunication through a wired connection. Accordingly, telemetry module66 may include circuitry known in the art for such communication.Examples of local wireless communication techniques that may be employedto facilitate communication between programmer 20 and another computingdevice include RF communication according to the 802.11 or Bluetoothspecification sets, infrared communication, e.g., according to the IrDAstandard, or other standard or proprietary telemetry protocols. In thismanner, other external devices may be capable of communicating withprogrammer 20 without needing to establish a secure wireless connection.

Power source 68 delivers operating power to the components of programmer20. Power source 68 may include a battery and a power generation circuitto produce the operating power. In some examples, the battery may berechargeable to allow extended operation. Recharging may be accomplishedthrough proximal inductive interaction, or electrical contact withcircuitry of a base or recharging station. In other examples, primarybatteries (e.g., nickel cadmium or lithium ion batteries) may be used.In addition, programmer 20 may be directly coupled to an alternatingcurrent source, such would be the case with some computing devices, suchas personal computers. Power source 68 may include circuitry to monitorpower remaining within a battery. In this manner, user interface 64 mayprovide a current battery level indicator or low battery level indicatorwhen the battery needs to be replaced or recharged. In some cases, powersource 68 may be capable of estimating the remaining time of operationusing the current battery.

FIGS. 4A-4C and 5 are flowcharts illustrating example techniques formodifying values for one or more types of therapy parameters of atherapy program based on an algorithmic model of a therapy field. Whilethe therapy parameter modification techniques shown in FIGS. 4A-4C and 5are described as being performed by programmer 20, in other examples,processor 40 (FIG. 2) of IMD 14 or a processor of another computingdevice, such as a clinician workstation, or any combination of devicesmay execute the techniques for modifying therapy parameters shown inFIGS. 4A-4C and 5.

As illustrated in FIG. 4A, programmer 20 generates a therapy program tocontrol therapy delivery to patient 12 by IMD 14 (70). In some examples,programmer 20 may facilitate evaluation of one or more therapy parametervalues in order to generate the therapy program. For example, memory 62of programmer 20 may store an evaluation sequence that guides the userin the selection of electrode combinations and stimulation parametervalues, or automatically selects electrode combinations and stimulationparameter values for evaluation of efficacy. For example, the evaluationsequence may specify a predetermined progression of electrodecombinations to be selected for evaluation, or provide rules for dynamicselection of electrode combinations during the course of evaluation.

Memory 62 also may record efficacy information associated with one ormore of the tested programs. Specifically, upon selection of anelectrode combination and stimulation parameters as a program,programmer 20 may direct IMD 14 to apply the program. Upon applicationof the program, the patient may provide feedback concerning efficacy.The user, which may be a clinician or the patient 12, then records theefficacy information in memory 62 of programmer 20. In this manner,different programs may be rated in terms of efficacy so that the userultimately may select an effective electrode combination and stimulationparameters.

After determining a therapy program for patient 12 (70), processor 60may generate an algorithmic model of a therapy field for the selectedtherapy program, e.g., a therapy program that, based on the ratinginformation, provides efficacious therapy to patient 12 (71). Thealgorithmic model of the therapy field represents where therapy willpropagate from therapy system 30 when IMD 14 is delivering therapy topatient 12 according to the selected therapy program. Electricalstimulation delivered by IMD 14 generates a therapy field within patient12. For example, the therapy field may be an electrical field thatindicates areas of the patient's tissue that are covered by anelectrical field emanating from electrodes 35, 37 of leads 34, 36 duringtherapy delivery. As another example, the therapy field may indicate anactivation field that indicates the neurons that are activated by theelectrical field. Accordingly, in some examples, the therapy field modelmay represent the electrical field or the activation field resultingfrom therapy delivery by therapy system 30 according to the selectedtherapy program.

The therapy field model may vary depending upon the therapy parametervalues of the selected therapy program and the patient anatomy proximateto the target tissue site for the electrical stimulation. For example,depending on the target tissue site for stimulation, an electrical fieldresulting from stimulation therapy delivered according to a particulartherapy program may have a different stimulation area, a differentcentroid of stimulation, or different activated neurons. As one example,the type of neurons activated may depend upon the patient anatomyproximate to the target tissue site for the stimulation, and thestimulation parameter values may be configured to target neurons lessthan a maximum diameter. The algorithm implemented by processor 60 togenerate the therapy field model, therefore, considers the therapyparameter values of the selected therapy program, the anatomy of patient12 proximate to the target stimulation site, and the hardwarecharacteristics of therapy system 30. In general, the electrical fieldmodel or the activation field model may estimate the anatomicalstructures that will be affected by a therapy program.

Processor 60 determines therapy guidelines based on the patientcondition (72). In one example, the therapy guidelines comprise areference therapy field that is specific to a patient condition. Thereference therapy field may be a therapy field that is believed toprovide efficacious therapy to manage the patient's condition, and maybe, but need not be, specific to the particular patient 12. In otherexamples, the reference therapy field may merely be a starting point forgenerating a therapy program for patient 12.

The therapy guidelines may provide guidelines for generating anefficacious therapy program for a particular patient within a patientclass characterized by a common patient condition. For example, thereference therapy field may define one or more field characteristicsthat the clinician may use as reference points for achieving aparticular functional outcome for the therapy delivery to patient 12.The field characteristics of a therapy field may include, but are notlimited to, centroids of stimulation, the total volume of the electricalfield or activation field (or the total area with respect to across-section of the therapy field), the regions of the patient anatomyrecruited or otherwise covered by the therapy field, a charge density oran amplitude of the voltage or current at a certain point within thestimulation therapy field, e.g., whether the voltage or currentamplitude at a certain point within the stimulation therapy fieldexceeds the activation energy of the neurons. Functional outcomes mayinclude, for example, mitigation of one or more symptoms associated withthe patient's condition. In the case of a seizure disorder, thefunctional outcomes may include the minimization of the frequency,severity, and/or duration of seizures. In the case of movementdisorders, the functional outcomes may include an improvement in thepatient's gait and mobility.

In addition to including one or more reference therapy fields, thetherapy guidelines may identify anatomical structures or target tissuesites within brain 18 (FIG. 1A) that may be activated by an electricalfield in order to effectively manage the patient's condition. Forexample, the therapy guidelines may identify the Substantia Nigra inbrain 18 as a useful target tissue site for electrical stimulationtherapy in order to reduce the number and magnitude of tremorsexperienced by patient 12. As another example, the therapy guidelinesmay identify the anterior thalamus, ventrolateral thalamus, globuspallidus, substantia nigra pars reticulata, subthalamic nucleus,neostriatum, cingulated gyms or the cingulate gyms as target tissuesites within brain 18 for managing a seizure disorder of patient 12.

In other examples, the therapy guidelines may provide information thatguides the programming of IMD 14 for other therapeutic applications. Forexample, with respect to therapy system 10 that provides spinal cordstimulation (SCS) to patient 12, the therapy guidelines may identify aparticular target tissue site proximate to a particular vertebra ofspinal cord 32 (FIG. 1B) for managing pain in a particular area, such asa particular class of back pain. As another example, if IMD 14 is usedto provide electrical stimulation therapy for managing urinary or fecalincontinence of patient 12, the therapy guidelines may identify therelevant nerve (e.g., a sacral nerve or pudendal nerve or nerve branch)or muscle for stimulating.

The therapy guidelines may be determined based on the results ofclinical studies, computer modeling or both. The therapy guidelines maybe stored within memory 62 of programmer 20, memory 42 of IMD 14, or amemory of another computing device. In some examples, a clinician orother user may upload the therapy guidelines into programmer 20 from aseparate computing device via telemetry interface 66. For example, aclinician may access a database of therapy guidelines with a computerworkstation, and, based on the symptoms of patient 12, select theappropriate therapy guidelines from the database and upload the selectedtherapy guidelines to programmer 20.

Processor 60 may compare the therapy field model to the referencetherapy field (73). In one example, processor 60 compares at least onefield characteristic of the modeled therapy field to a respectivecharacteristic of the reference therapy field. The one or more comparedfield characteristics may be selected based on the characteristics ofthe therapy field that may affect the efficacy of therapy. In addition,the field characteristics may be weighted based on their impact on theefficacy of therapy, and the comparison between the algorithmic modelsof the original therapy field and the adjusted therapy field may be madeon the weighted field characteristics.

In the case of DBS delivered by therapy system 10 (FIG. 1A), the regionsof the patient anatomy recruited or otherwise covered by the therapyfield may affect the efficacy of therapy more than the total volume ofthe electrical field or activation field. Thus, processor 60 may comparethe regions of patient anatomy recruited or otherwise covered by thetherapy field model that was generated based on the therapy program withthe regions of patient anatomy recruited or otherwise covered by thereference therapy field in order to determine whether to modify thetherapy program. However, in some cases, processor 60 may compare boththe regions of patient anatomy recruited by the modeled therapy field aswell as the total volumes of the electrical field or activation fieldwith the respective characteristics of the reference therapy field.

In the case of SCS delivered by therapy system 30 (FIG. 1B), thecentroid of stimulation may affect the efficacy of therapy more than thetotal volume of the electrical field or activation field. Thus,processor 60 may compare the centroid of stimulation of the therapyfield model based on the therapy program with the centroid ofstimulation of the reference therapy field in order to determine whetherto modify the therapy program. Again, processor 60 may compare more thanone field characteristics of the current therapy field with thereference therapy field.

In some examples, processor 60 computes one or more metrics thatindicate the similarity between the therapy field model that wasgenerated based on the therapy program and the reference field definedby the therapy guidelines. As one example, processor 60 may determinethe ratio of the volume of the reference therapy field to the volume ofthe therapy field model. Other metrics may include the percentage ofoverlap between the reference field and the therapy field model, or thetotal volume of the therapy field model that does or does not overlapthe reference field.

In some examples, processor 60 presents the therapy field modelgenerated based on the therapy program and the reference therapy fieldof the therapy guidelines on the display of user interface 64 ofprogrammer 20. For example, as will be described in further detailbelow, the modeled and reference therapy fields may be overlaid on arepresentation of the target anatomical region of patient 12 for thetherapy delivery. A user may visually or otherwise compare the displayedfields and provide feedback to processor 60 via user interface 64.

Based on the comparison between the therapy field model and thereference field, processor 60 may adjust one or more therapy parametervalues, e.g., respective values for the pulse width, frequency oramplitude defined by the therapy program (74). For example, if thevolume of the therapy field model is substantially larger than thevolume of the reference therapy field, the clinician or another user ofprogrammer 20 may adjust one or more therapy parameter values togenerate a smaller therapy field. Processor 60 may suggest a parameteradjustment to a user via user interface 64 or automatically adjust oneor more therapy parameters based on the calculated metrics. Memory 62 ofprogrammer 20 may include, for example, a set of therapy parameter valuemodification rules that enables processor 60 determine how the therapyfield may be modified (e.g., decreased in volume). In some examples,processor 60 compares a metric indicative of the ratio between thevolume of the therapy field model generated based on the therapy programand the volume of the reference field to a threshold value and adjuststhe therapy program based on the comparison. Memory 62 may store themetric values determined by processor 60 based on the comparison betweenthe therapy field model and the reference field, as well as any relevantthreshold values and rules for therapy program modification.

In some examples, after processor 60 modifies the therapy program,processor 60 may generate an algorithmic model of the modified therapyfield (“modified therapy field model”) resulting from therapy deliveryby therapy system 10 according to the modified therapy program definingthe adjusted set of therapy parameter values. The algorithmic model ofthe modified therapy field may be generated using the same or adifferent algorithm that is used to generate the algorithmic model ofthe therapy field resulting from therapy delivery according to thetherapy program. In some examples, the modified therapy field modelproduced by the adjusted set of therapy parameter values may moreclosely resemble the reference field. If the first therapy field modelbased on the first therapy program has a volume substantially largerthan the reference therapy field, the modified therapy field that isbased on the modified therapy program may be have a smaller volume thanthe first therapy field model, which may be closer to the volume to thereference field than the first therapy field model. An algorithmic modelof a therapy field with a volume substantially larger than the referencefield may indicate that the stimulation energy used to providestimulation therapy to patient 12 is higher than necessary to manage thepatient condition, which may result in wasted energy and potentiallycause long term nerve damage. Decreasing the volume of the therapy fieldmodel may help minimize the stimulation energy that is required toprovide the stimulation therapy to patient 12. In this way, themodification to the therapy program may promote long-term therapeuticoutcomes and patient comfort by increasing the useful life of IMD 14 andits power source 50 (FIG. 2).

After processor 60 modifies the therapy program and generates analgorithmic model of the modified therapy field based on the modifiedtherapy program, processor 60 may perform an additional comparisonbetween the modified therapy field and the reference field to determineif further modification to the modified therapy program is desirable.For example, processor 60 may compare the algorithmic model of themodified therapy field to the reference therapy field (73) and adjusttherapy parameter values based on the comparison (74).

In some examples, rather than generating a therapy program (70),processor 60 of programmer 20 may merely select a therapy program frommemory 62 of programmer 20 or memory 42 (FIG. 2) of IMD 14. The therapyprogram may be, for example, identified as being a potentiallyefficacious therapy program for patient 12 during a prior programmingsession. As another example, processor 60 may select a therapy programthat has been identified as being a potentially efficacious therapyprogram for a class of patients having the same patient condition aspatient 12.

FIG. 4B illustrates another example of a technique for modifying atherapy program based on an algorithmic model of a therapy field andtherapy guidelines. The technique outlined in FIG. 4B is similar to themethod outlined to FIG. 4A. However, in the example techniqueillustrated in FIG. 4B, the determination of the therapy guidelines isbased on one or more patient events that are detected when therapy isdelivered to patient 12 using the therapy program.

As described with respect to FIG. 4A, processor 60 of programmer 20 maygenerate or select a therapy program (70) and generate an algorithmicmodel of a therapy field based on the therapy program (71).Additionally, processor 60 may control IMD 14 to deliver therapy topatient 12 according to the therapy program (80). During therapydelivery, processor 60 may monitor one or more physiological parametersof patient 12 based on signals from one or more sensors 26 (FIG. 1A) inorder to detect one or more patient events based on the signals (82).Patient events may, for example, reflect the occurrence of patientsymptoms associated with the patient condition for which therapy systems10, 30 are implemented to manage or side effects from the therapydelivery.

If the stimulation intensity is too low, the patient may experiencesymptoms associated with the patient condition for which therapy systems10, 30 are implemented to manage. If the stimulation intensity is toohigh, the patient may experience side effects, such as pain. Thedetection of patient events may indicate that therapy delivery accordingto the current therapy program is not providing efficacious treatment ofthe patient condition, e.g., because the events may indicate undesirablethe patient symptoms or side effects. Processor 60 may determine whetherthe current therapy program is providing efficacious therapy to patient12 based on the detected patient events (83).

In some examples, patient 12 may provide feedback, e.g., via programmer20, relating to the occurrence of a patient event. Feedback from patient12 may be useful if sensor 26 does not detect the patient event and/orthe feedback is a subjective assessment provided by patient 12. Forexample, in one example, programmer 20 includes a dedicated button oranother user input mechanism that patient 12 may press or otherwiseinteract with each time a particular patient event occurs, such as aseizure, a pain level above a particular threshold (which may besubjectively assessed by patient 12), an incontinence event, anuncomfortable response to stimulation, or a stimulation signal thatcovers a non-target region. The patient event may be selected to be asymptom of the patient condition for which the therapy system is used totreat or a side effect of the electrical stimulation therapy. Processor60 may store an indication, such as a flag, value or signal, uponactivation of the event button (or other input mechanism). Upon reachinga threshold number within a particular time frame (e.g., an hour, days,weeks or months), processor 60 may evaluate the therapy program due tothe detected patient events.

Instead of or in addition to patient input to provide informationrelating to the occurrence of patient events during therapy deliveryaccording to the current therapy program, information from sensors mayprovide information regarding the occurrence of patient events. Asdiscussed above, therapy systems 10, 30 may include one or more sensors,such as sensor 26 or a sensor on IMD 14 housing or coupled to leads 16,34, 36, which may monitor a patient parameter that changes in responseto the efficacy of therapy, such as in response to an increase inpatient symptoms or an increase in patient side effects. For example, iftherapy system 10 delivers therapy to manage a seizure disorder ofpatient 12, sensor 26 may include an accelerometer (e.g., one or moreone, two or three axis accelerometers), a bonded piezoelectric crystal,a mercury switch, or a gyro to monitor patient activity level to detectthe occurrence of a seizure, e.g., by detecting the abnormal bodymovements. In yet another example, sensor 26 may monitor a heart rate ofpatient 12, and a change in heart rate may indicate an onset of aseizure.

Sensing electrodes on leads 16, 34, 36 may also be used to detect theoccurrence of a seizure, e.g., based on EEG or ECoG signals or otherbrain signals. Processor 60 of programmer 20 may receive the signalsfrom the sensing electrodes or sensor 26 and determine whether thesignals indicate the occurrence of a seizure. For example, processor 60may compare the EEG or ECoG waveform to a threshold amplitude value thatindicates a seizure occurred, or processor 60 may perform a temporalcorrelation or frequency correlation with a template signal, orcombinations thereof in order to determine whether a seizure hasoccurred. Alternatively, processor 40 of IMD 14 may determine whether aseizure occurred and transmit an indication, such as a flag, value orother marker, to programmer 20. In general, for each example describedherein, processor 40 of IMD 14 may detect a patient event and transmitan indication to programmer 20.

Processor 60 may record each seizure occurrence, and upon reaching athreshold number of seizures within a particular time frame (e.g., anhour, days, weeks or months) or a particular pattern of seizures,processor 60 may determine that the therapy is not substantiallyeffective due to the increase in the number of seizures experienced bypatient 12. Thus, a certain number of seizure events may promptprocessor 60 to evaluate the current therapy field.

In examples in which therapy system 10 (FIG. 1A) provides DBS to managea movement or mood disorder (e.g., a psychiatric disorder) of patient12, the activity level of patient 12 may be monitored to detect patientevents. For example, a decreased activity level may indicate thatpatient 12 is experiencing increased tremors or is in a depressive moodstate, and, therefore, the current therapy program may not be providingefficacious therapy to patient 12. Accordingly, in some examples, sensor26 may monitor various patient parameters that indicate a patientactivity level, such as heart rate, respiration rate, respiratoryvolume, core temperature, blood pressure, blood oxygen saturation,partial pressure of oxygen within blood, partial pressure of oxygenwithin cerebrospinal fluid, muscular activity, arterial blood flow, EMG,EEG, ECoG, and ECG. As another example, patient 12 may provide feedback,e.g., via programmer 20, relating to the occurrence of side effects,such as cognitive and/or psychiatric (e.g., changes in mood state) sideeffects.

Processor 40 of IMD 14 or processor 60 of programmer 20 may determineactivity counts for patient 12 while therapy is delivered to patient 12according to the current therapy program, and associate the activitycounts with the current therapy program. Examples of determiningactivity counts and associating activity counts with therapy programsare described in U.S. Pat. No. 7,395,113 issued on Jul. 1, 2008 toHeruth et al., which is entitled, “COLLECTING ACTIVITY INFORMATION TOEVALUATE THERAPY,” and was filed on Apr. 15, 2004. As described in U.S.Pat. No. 7,395,113 to Heruth et al., processor 40 of IMD 14 or processor60 of programmer 20 may determine a number of activity counts based onsignals generated by sensor 26, and the number of activity counts may bestored as an activity level associated with the current therapy program.For example, the number of activity counts may be a number of thresholdcrossings by a signal generated by sensor 26, such as an accelerometeror piezoelectric crystal, during a sample period, or a number of switchcontacts indicated by the signal generated by sensor 26, such as mercuryswitch during a sample period. Upon determining that the activity level(or the number of activity counts) falls below a particular thresholdlevel for a certain time range, such as one or more hours, days orweeks, processor 40 or 60 may determine that the current therapy programis not providing efficacious therapy to patient 12.

In examples in which therapy system 10 provides DBS to manage a mooddisorder, such as bipolar disorder or major depressive disorder, ofpatient 12, or therapy system 30 provides SCS to manage the patient'spain, the sleep quality of patient 12 may indicate the efficacy oftherapy. For example, if patient 12 is afflicted with bipolar disorderor major depressive disorder, poor sleep quality may indicate insomniaor a manic mood state. The insomnia or manic mood state may be a symptomof the patient's condition or side effect of the therapy deliveryaccording to the current therapy program.

The quality of the patient's sleep may be determined using any suitabletechnique. In one example, processor 40 of IMD 14 determines values ofone or more sleep metrics that indicate a probability of a patient beingasleep based on the current value of one or more physiologicalparameters of the patient, as described in U.S. Patent ApplicationPublication No. 2005/0209512 by Heruth et al., which is entitled,“DETECTING SLEEP” and was filed on Apr. 15, 2004. Processor 40 may thendetermine the number of disruptions in the patient's sleep, e.g., basedon the number of times processor 40 determines patient 12 is not asleepduring a particular time frame (e.g., 10 p.m. to about 8 a.m.).

As described in U.S. Patent Application Publication No. 2005/0209512 byHeruth et al., sensor 26 may generate a signal as a function of at leastone physiological parameter of a patient that may discernibly changewhen the patient is asleep. Examples of suitable physiologicalparameters include activity level, posture, heart rate, respirationrate, respiratory volume, blood pressure, blood oxygen saturation,partial pressure of oxygen within blood, partial pressure of oxygenwithin cerebrospinal fluid, muscular activity, core temperature,arterial blood flow, and galvanic skin response. In some examples, theprocessor determines a value of a sleep metric that indicates aprobability of the patient being asleep based on a physiologicalparameter. In particular, the processor may apply a function or look-uptable to the current value and/or variability of the physiologicalparameter to determine the sleep metric value. The processor may comparethe sleep metric value to a threshold value to determine whether thepatient is asleep.

In some examples, a therapy system may be configured to deliverelectrical stimulation therapy to patient 12 in order to manage urinaryor fecal incontinence. In such cases, sensor 26 may be positioned todetect the occurrence of an involuntary urinary or fecal voiding eventor urinary or fecal retention. In the case of fecal incontinence, sensor26 may additionally or alternatively detect the occurrence of a loosebowel movement. Sensor 26 may provide the signals to programmer 20, andprocessor 60 may evaluate the efficacy of the current therapy programbased on the number of involuntary voiding events associated with thecurrent therapy program. Sensor 26 may, for example, detect a voidingevent by detecting nerve impulses of a sacral or pudendal nerve, asdescribed in U.S. Patent Application Publication No. 2007/0255176 byRondoni et al., which was filed on Apr. 28, 2006 and is entitled,“VOIDING DETECTION WITH LEARNING MODE.” As other non-limiting examples,sensor 26 may be disposed adjacent to patient 12 via an undergarmentworn by patient 12, and may be configured to detect the presence offluid, which may indicate that an involuntary voiding event hasoccurred. For example, as described in U.S. Pat. No. 7,855,653 issued onDec. 21, 2010 to Rondoni et al., which was filed on Apr. 28, 2006 and isentitled, “EXTERNAL VOIDING SENSOR SYSTEM,” sensor 26 may determinewetness by detecting a decrease in resistance between two electrodes ofthe sensor, or by detecting fluid pH, impedance, electrolyteconcentration, or other characteristics of the fluid to identify thatthe fluid is urine.

Processor 60 may compare the total number of involuntary voiding eventsthat occurred during therapy delivery via the current therapy programwith a threshold value, which may be stored in memory 62. In otherexamples, processor 60 may compare the average number of voiding eventsfor a sample period of time (e.g., average number of voiding events perday or week) with a threshold value. Upon crossing the threshold,processor 60 may determine that the current therapy program is notproviding efficacious therapy to patient 12.

As other examples, in order to indicate the efficacy of the currenttherapy program in managing urinary incontinence, sensor 26 may beconfigured to provide information relating to the function of thebladder of patient 12, or any other segment of the patient's urinarytract, in storing, releasing, and passing urine. For example, asdescribed in U.S. Patent Application Publication No. 2007/0100388 byGerber, which was filed on Oct. 31, 2005 and is entitled, “IMPLANTABLEMEDICAL DEVICE PROVIDING ADAPTIVE NEUROSTIMULATION THERAPY FORINCONTINENCE,” sensor 26 may monitor patient parameters such as bladderpressure, bladder contractile force, urinary sphincter pressure, urineflow rate, urine flow pressure, voiding amount, and the like. Theseurodynamic parameters of patient 12 may indicate the efficacy of thecurrent therapy program. The urodynamic parameters may, but do notnecessarily indicate the occurrence of an involuntary voiding event.

In other examples, sensor 26 or other sensing devices may provide anysuitable information to detect patient events that indicate therapyefficacy. The patient parameters that sensor 26 monitors may differdepending upon the patient condition for which the therapy program isimplemented to manage.

If processor 60 determines that the current therapy program is providingefficacious to patient 12 based on the detected patient events (83),e.g., if no patient events detected or if the less than a thresholdnumber of events are detected, processor 60 may continue monitoringsignals from sensor 26 or IMD 14 to determine whether patient eventshave occurred (82). In addition, IMD 14 may continue delivering therapyaccording to the therapy program (80).

On the other hand, if processor 60 determines the current therapyprogram is not efficacious (83), processor 60 may reference therapyguidelines for the patient condition, where the therapy guidelinesdefine a reference therapy field (72). As in the technique shown in FIG.4A, processor 60 may determine therapy guidelines based on the detectedpatient event and the patient condition. For example, processor 60 mayselect therapy guidelines with functional outcomes directed towarddecreasing the type of patient events detected. As previously described,the therapy guidelines include one or more reference therapy fields withknown efficacy for treating a patient condition (e.g., a particulardisease state), or producing a particular therapeutic outcome. Processor60 may compare the algorithmic model of the therapy field based on thecurrent therapy program to the reference field of the therapy guidelines(73) to determine what, if any, modifications should be made to thecurrent therapy program. Processor 60 may then modify values of one ormore therapy parameters of the therapy program based on the comparisonbetween the algorithmic model of the therapy field and the referencetherapy field (74). In this way, the therapy guidelines provideinformation that help a user modify a therapy program.

In some examples, processor 60 of programmer 20 may monitor therapeuticefficacy when therapy is delivered to patient 12 according to themodified therapy program including the adjusted therapy parametervalues, as illustrated in FIG. 4C. The technique shown in FIG. 4C may beperformed after the therapy program is modified based on the comparisonbetween the algorithmic model of the therapy field and the referencetherapy field (74), as described with reference to FIGS. 4A and 4B.Processor 60 may deliver therapy to patient 12 according to the modifiedtherapy program (75) and monitor a signal indicative of a patientparameter (76), which may be a signal generated by sensor 26 or IMD 14.Processor 60 may detect a patient event based on the signal (82), asdescribed above with respect to FIG. 4B. The patient event may reflectthe occurrence of patient symptoms associated with the patient conditionfor which the therapy system is implemented or side effects from thetherapy delivery, as examples. The detection of patient events mayindicate that the therapy is not providing efficacious treatment of thepatient condition.

Upon detection of a patient event, processor 60 may analyze thepreviously determined (e.g., previously selected or generated) therapyguidelines (77). Processor 60 may, for example, determine whether thepreviously-determined therapy guidelines are still applicable to thepatient condition (78). The detected patient events may indicate thatthe patient's condition has changed, e.g., has worsened, and that adifferent set of therapy guidelines may provide more useful informationfor defining an efficacious therapy program for patient 12. In somecases, different degrees of progression or severity of a patientcondition may be associated with different therapy guidelines.Accordingly, in one example, upon detection of a patient event (82) anda determination that the therapy guidelines are no longer applicable tothe patient condition (78), processor 60 determines (e.g., selects) adifferent set of therapy guidelines (79). Processor 60 may determinethat the previously-determined therapy guidelines are no longer bestapplicable to the patient condition relative to other therapy guidelinesthat may be selected. Thus, in other examples, processor 60 may analyzedetermined therapy guidelines (78) and verify that the selected therapyguidelines are bested suited for the patient condition compared to otheravailable therapy guidelines.

After selecting another set of therapy guidelines (79) or determiningthat the previously-determined therapy guidelines are applicable to thepatient condition (78), processor 60 generates an algorithmic model of atherapy field based on the modified therapy program (87). Processor 60may also compare the therapy guidelines and the algorithmic field model(88) and modify the modified therapy program based on the comparison. Inthis manner, processor 60 may further modify the modified therapyprogram to generate a different stimulation field based on the therapyguidelines determined to be applicable to the patient condition. Forexample, if different therapy guidelines were determined to beapplicable to the patient condition based on the detected patient event(78, 79), processor 60 may modify the modified therapy program togenerate a different stimulation field based on the new set of therapyguidelines. As another example, if the originally-determined therapyguidelines were determined to be still applicable to the patientcondition based on the detected patient event (78), processor 60 mayincrease the strength of the stimulation (e.g., by increasing a voltageor current amplitude and/or duration of the stimulation) to increase thesize of the stimulation field.

FIG. 5 is a flow diagram illustrating another example technique formodifying one or more therapy parameter values based on an algorithmicmodel of a therapy field. As described with respect to technique shownin FIG. 4A, processor 60 of programmer 20 may generate (or select) atherapy program comprising a set of therapy parameter values forcontrolling therapy delivery by IMD 14 (70). Processor 60 may generatean algorithmic model of a therapy field based on the therapy program(71). In some examples, programmer 20 facilitates evaluation of multipletherapy programs, and processor 60 generates an algorithmic model foreach of the therapy programs. The plurality of therapy program may be,for example, therapy programs that, as indicated by rating informationreceived during a trialing session, provide efficacious therapy topatient 12.

Once an algorithmic model of the therapy field corresponding to thetherapy program is generated, processor 60 may analyze the efficiency oftherapy system 10 when therapy is delivered according to the therapyprogram (84). For example, processor 60 may access operating efficiencydata, e.g., stored within memory 62 of programmer 20 and/or stored inanother computing device or IMD 14 and accessed via telemetry interface66. The operating efficiency data may relate to operating ranges oftherapy system 10, and may be specific to, for example, a condition ofpatient 12, a desired therapeutic outcome, the target tissue site fortherapy delivery, the anatomy of patient 12, and/or tissue-specificproperties. In one example, the operating efficiency data definesguidelines that enable processor 60 or a user to modify one or moretherapy parameter values of a therapy program to improve the energyefficiency of IMD 14 while substantially maintaining at least one fieldcharacteristic of a therapy field model generated based on the therapyprogram.

As one example, processor 60 may access a strength duration curveassociated with a condition of patient 12. A strength-duration curve maydescribe the relationship between a strength of stimulation andduration, e.g., for a particular neurological response. The strength ofstimulation may be a function of, for example, any one or more of thevoltage or current amplitude value of the stimulation signal, frequencyof stimulation signals, signal duration (e.g., pulse width in the caseof stimulation pulses), signal burst pattern, and the like. An exampleof a strength duration curve is an amplitude-duration curve associatedwith a condition of patient 12. The amplitude-duration curve may reflectdifferent combinations of amplitude and duration (e.g., pulse width in acase of stimulation pulses) values that contribute to the therapy fieldin a substantially similar manner. In this way, the amplitude-durationcurve may describe different combinations of amplitudes and durationsthat elicit substantially similar to the same neurological responses.For example, the strength-duration curve may indicate that a loweramplitude stimulation pulse with a longer duration may elicitsubstantially the same neurological response as a higher amplitude pulsewith a narrower pulse width.

Each position on the amplitude-duration curve, or each position within aparticular range of positions along the amplitude-duration curve, mayresult in a substantially similar therapy field when the other therapyparameters remain substantially constant (e.g., the other therapyparameter values may remain within a particular range of therapyparameter values, such as within a 10% window or less from the valuesdefined by the therapy program). As described in further detail below,different combinations of therapy parameter values that producesubstantially similar therapy fields may require different levels ofpower consumption by IMD 14.

Processor 60 may also analyze the efficiency of therapy system 10 whentherapy is delivered according to the therapy program by evaluating theamplitude of the stimulation signal based on the multiplier levelsallowed by IMD 14. The multiplier levels may be used in conjunction witha strength-duration curve to analyze the efficiency of therapy system10. IMD 14 may include a capacitor module that is configurable to storevarious voltages, i.e., various multiples of the voltage of power source50 (FIG. 2). In one example, based on the selected configuration of thecapacitor module, the capacitor module may output a voltage less than,equal to, or greater than the voltage supplied by power source 50.Processor 40 of IMD 14 may configure the capacitor module to store avoltage appropriate for the voltage or current amplitude specified bythe therapy program. The capacitor module may include a plurality ofcapacitors and switches that processor 40 configures to store theappropriate voltage. Because the voltages that the capacitor module iscapable of storing are limited by the possible configurations of thecapacitors and switches, the capacitor module is capable of storing afinite number of discrete voltages.

Processor 40 of IMD 16 may configure the capacitor module to store avoltage that is sufficient to produce the amplitude specified by thetherapy program. The stored voltage may be greater than the voltagenecessary to produce the specified amplitude due to the limitations onthe voltage values that the capacitor module can store. If the voltagestored by the capacitor module is greater than the voltage necessary toproduce the amplitude specified by the therapy program, excess energythat is not used to produce the stimulation output is pulled from powersource 50. Energy efficiency of IMD 14 may be increased the closer thevoltage stored by the capacitor module is to the voltage necessary toproduce the amplitude specified by the therapy program. Thus, to achievemaximum energy efficiency, the voltage stored by the capacitor moduleshould typically equal the voltage necessary to produce the amplitudespecified by the therapy program. Processor 60 of programmer 20 maycompare the voltage necessary to produce the current or voltageamplitude specified by the therapy program to the multiplier levelsallowed by the capacitor module of IMD 14 to evaluate energy efficiency.When the voltage required to produce the stimulation amplitude isbetween multiplier levels allowed by the capacitor module of IMD 14, IMD14 does not operate at maximum efficiency.

Processor 60 may select an amplitude of a stimulation signal to increasethe operating efficiency of IMD 14 based on the multiplier levels IMD 14is configured to operate with, and select a duration, e.g., pulse width,appropriate for the desired stimulation intensity based anamplitude-duration curve or other operating efficiency data. Forexample, processor 60 may decrease an amplitude of a stimulation signalsuch that the voltage stored by the capacitor module is substantiallyequal to the voltage necessary to produce the amplitude and increase aduration of the stimulation signal in an amount determined from theamplitude-duration curve. As another example, processor 60 may increasean amplitude of a stimulation signal such that the voltage stored by thecapacitor module is substantially equal to the voltage necessary toproduce the amplitude and decrease a duration of the stimulation signalin an amount determined from the amplitude-duration curve. In otherwords, processor 60 may decrease a stimulation amplitude to allow use ofa lower multiplier level with an increased duration or increase astimulation amplitude to allow more efficient use of a higher multiplierlevel with a decreased duration. In this manner, processor 60 may adjustvalues of stimulation parameters to allow IMD 14 to generate thestimulation output more efficiency while providing substantially thesame amount of stimulation energy to the patient and elicitingsubstantially the same patient response.

The amount of excess energy pulled from power source 50 of IMD 14 thatis not used to produce a current or voltage stimulation amplitude isdependent upon the relationship between the voltage required to producethe stimulation amplitude and the multiplier level used to produce theamplitude. Using a higher multiplier level requires more energy frompower source 50 than using a lower multiplier level. If the voltagerequired to produce a desired amplitude is larger than the voltageproduced at a first, lower multiplier level, a second, higher multiplierlevel must be used. However, if the voltage required to produce thedesired amplitude is only slightly larger than the voltage produced athe first, lower multiplier level, only a small portion of the energythat is pulled from power source 50 to go from the first, lowermultiplier level to the second, higher multiplier level is used toproduce the desired amplitude. The rest of the energy pulled from powersource 50 to move to the next, higher multiplier level may, therefore,be excess energy that is not used to produce the stimulation amplitude.Therefore, decreasing an amplitude of a therapy program to operate at alower multiplier level may significantly impact operating efficiency ofthe therapy system. The concept of decreasing an amplitude of a therapyprogram to operate at a lower multiplier level may also be referred toas avoiding operating above a voltage multiplier level.

Other types of operating efficiency data may include, for example,dose-response curves or three-dimensional (3D) depolarization fieldmodels. A dose response curve may provide information regarding generaltherapy outcomes, such as information regarding the amount ofstimulation required to provide a particular therapeutic outcome. Insome examples, a dose of stimulation is characterized by the intensityof stimulation, which may be affected by variables such as the voltageor current amplitude, signal duration (e.g., pulse width) or frequencyof signal delivery defined by a therapy program, or a signal burstpattern of stimulation delivery. As one example, the dose response curvemay specify that therapy should be delivered for about ten minutes perhour to provide efficacious therapy.

A dose response curve may also indicate a range of therapy parametervalues that typically provide efficacious therapy. For example, a doseresponse curve may be used to predict whether changing a value of aparticular therapy parameter in a particular direction (e.g., up ordown, thereby increasing or decreasing, respectively, the dose of thetherapy delivery) impacts therapy efficacy, and, in some cases, theextent to which therapy efficacy is impacted by the change to thetherapy parameter value. If the dose response curve predicts that thetherapy efficacy would remain unchanged within a particular range oftherapy parameter values, the therapy parameter values of a therapyprogram for patient 12 may be changed to be within that range to improveefficiency of the therapy system without impacting therapy efficacy. Asone example, a dose response curve may indicate that decreasing astimulation frequency from a value greater than approximately 100 Hz toa value that is approximately 100 Hz will not impact the efficacy of DBStherapy.

A depolarization curve may describe the relationship between stimulationparameter values and the volume of tissue that is affected, e.g.,depolarized. For example, 3D depolarization field models may indicatewhich anatomical structures are likely being activated and the extent ofthe activation. Processor 60 may select therapy parameter values thatincrease an operating efficiency of IMD 16 and maintain a specificvolume of tissue that is affected.

The amplitude-duration curve, as well as other types of operatingefficiency data, may be configured based on a condition (e.g., aparticular disease state) of patient 12, a desired therapeutic outcome,tissue conductivity of the target delivery site, and/or other tissueproperties of the target delivery site.

Based on the analysis of the data relating to the efficiency of therapysystem 10 and the therapy program, processor 60 may automaticallydetermine a second set of therapy parameters (i.e., a second therapyprogram) that increase an operating efficiency of therapy system 10while substantially maintaining one or more characteristics of thetherapy field (86). In some cases, processor 60 may reconfigure theactive electrodes of leads 34, 36 and/or change other therapy parametervalues to generate a therapy program that increases the operatingefficiency of therapy system 10, but substantially maintains thetherapeutic effects of the previously-selected therapy program. In someexamples, processor 60 may adjust the therapy parameters to decrease thepower consumption of IMD 14 and/or avoid operating between voltagemultiplier levels of IMD 14. As one example, processor 60 may identifythe position on the amplitude-duration curve that is most efficient forIMD 14. Different combinations of therapy parameters that producesubstantially similar therapy fields may require different levels ofpower consumption by IMD 14. A small change in therapy parameter valuesmay result in significant changes in battery recharge frequency and/orlongevity. In some cases, it may be desirable to minimize powerconsumption by IMD 14 in order to increase the longevity of power supply50 (FIG. 2).

In some examples, processor 60 generates an algorithmic model of thetherapy field according to the second therapy program for comparison tothe algorithmic model of the therapy field according to the originaltherapy program. As described in further detail below with reference toFIG. 7, processor 60 may display both of the modeled therapy fields to auser via user interface 64, compare respective field characteristics ofthe modeled therapy fields, and/or compute a metric indicative of howclosely the therapy field model based on the second therapy programcompares to the therapy field model based on the original therapyprogram. In some examples, processor 60 determines that the therapyfield model based on the original therapy program is substantiallymaintained, if a difference, e.g., based on one or more fieldcharacteristics and/or metrics, between the therapy field modelgenerated according to the second therapy program and the originaltherapy field model is below a threshold. The threshold may, forexample, be selected by a clinician.

For example, processor 60 may compare the centroid of the originaltherapy field model with the centroid of the therapy field model basedon the second therapy program. If a distance between the two centroidsis less than a threshold value, processor 60 may determine that thetherapy field is substantially maintained, which suggests that thesecond therapy program may provide substantially similar efficacy as theoriginal therapy program. The threshold value may be stored withinmemory 62 and may be specific to a target stimulation site, a patientcondition, and/or patient 12. In some examples, processor 60 may comparemultiple field characteristics to respective threshold values todetermine whether the therapy field is substantially maintained. Asanother example, processor 60 compares a metric value indicative of howclosely the therapy field model based on the second therapy programresembles the original therapy field model to a threshold value todetermine whether the therapy field is substantially maintained. Examplemetrics include the percentage of overlap (e.g., volumetric overlap oroverlap in one or more cross-sections of the therapy field) between theoriginal therapy field model and the therapy field model based on thesecond therapy program, or the volume of the therapy field model basedon the second therapy program that does not overlap with the originaltherapy field model.

Substantially maintaining the one or more field characteristics of theoriginal therapy field model based on the original therapy program maybe desirable if the original therapy field model provides efficacioustherapy for managing a particular patient condition or produces aparticular therapeutic outcome. The process described with respect toFIG. 5 may allow the operating efficacy of therapy system 10, 30 to beincreased without substantially impacting therapeutic efficacy. In someexamples, processor 60 may first adjust the therapy parameter values ofthe original therapy program based on a reference therapy field definedby therapy guidelines, as described with respect to FIGS. 4A-4C, andsubsequently adjust the therapy parameter values to increase anoperating efficiency of therapy system 10, 30 while substantiallymaintaining the original therapy field, as described with respect toFIG. 5. By knowing the desired therapeutic outcome and the configurationof therapy system 10, a therapy program that helps to maximize theperformance of therapy system 10 and generate a therapy field that isbeneficial for the particular target tissue site, e.g., eliminate orminimize noxiousness and/or accommodation, may be determined.

FIGS. 6-16 illustrate various user interfaces and methods for generatingalgorithmic models of therapy fields and modifying therapy parametervalues of a therapy program based on the therapy field models. While theremainder of the description of FIGS. 6-16 primarily refers to therapysystem 10 of FIG. 1A including a single lead 16, in other examples, thetechniques for using therapy field models to guide modification oftherapy parameters may be applied to a therapy system including morethan one lead, as well as a therapy system implanted proximate to othertarget tissue sites, such as therapy system 30 of FIG. 1B that providesSCS to patient 12.

FIG. 6A illustrates an example graphical user interface (GUI) 90 thatmay be presented on the display of user interface 64 of programmer 20(FIG. 3) or another computing device to allow a user to select a set oftherapy guidelines based on a patient condition. GUI 90 presents theuser with a list of different types of patient conditions. In theexample illustrated in FIG. 6A, GUI 90 displays gastric disorders 92A,movement disorders 92B, pain disorders 92C, pelvic floor disorders 92D,psychiatric disorders 92E, and seizure disorders 92F (collectively“therapy categories 92”) for selection. In other examples, GUI 90 maypresent any number or type of therapy categories for selection.

In the example shown in FIG. 6A, GUI 90 includes selectable text boxesthat specify the different therapy categories 92. A user may determine(e.g., select) a therapy guideline by selecting the text box with astylet, a mouse or another peripheral pointing device, or by selecting abutton on programmer 20. In other examples, the list of therapycategories 92 may be presented in any suitable form. For example,therapy categories 92 may be presented by a drop down list or may beassociated with alphanumeric identifiers (e.g., categories “A” and “B”),and the user may input the alphanumeric identifier to select a therapycategory.

Upon selection of a therapy category 92 from GUI 90, programmer 20 maypresent GUI 100 relating to the selected therapy category. Asillustrated in FIG. 6B, GUI 100 may present the user with a listing ofdifferent disorders within the selected therapy category 92. In theexample illustrated in FIG. 6B, GUI 100 displays dystonia 102A,Parkinson's Disease 102B, and physiological tremor 102C within themovement disorder therapy category 92B. Again, although the disordersare presented as selectable text boxes, in other examples, the patientdisorders may be presented in any suitable form.

FIG. 6C illustrates an example GUI 110 that allows a user to viewtherapy guidelines for a particular patient condition. In the exampleillustrated in FIG. 6C, GUI 110 displays guidelines for Parkinson'sdisease 102B (FIG. 6B). In the example shown in FIG. 6C, the therapyguidelines include reference therapy fields 112, functional outcomes114, and target anatomical structures 116. The user may select any ofthe different types of information that make up the therapy guidelinesin order to view more information about the therapy guidelines. Thetypes of guideline information may be presented as selectable text boxesor via any suitable form.

The user may select reference therapy fields 112 in order to view moreinformation about the reference therapy fields that may have knownefficacy for treating a patient condition or producing a therapeuticoutcome for Parkinson's Disease. For example, as described with respectto FIG. 7, programmer 20 may present a visual representation of thereference therapy field relative to schematic illustrations of leadsand/or patient anatomy. The patient anatomy displayed with the referencetherapy fields may be specific to patient 12 or may be more general.

The user may select functional outcomes 114 to view a list of functionaloutcomes that may be achieved by using the selected therapy guidelinesfor Parkinson's disease, such as by generating a stimulation field thatis similar to the reference therapy fields or generating a stimulationfield that activates specific target anatomical structures 116 withinbrain 18. Accordingly, the functional outcomes 114 may be specific tothe selected therapy guidelines and may include, for example, mitigationof one or more symptoms associated with the patient's condition. Forexample, functional outcomes 114 of Parkinson's disease may include adecrease in resting tremors (e.g., in the frequency range ofapproximately 4 Hertz (Hz) to approximately 7 Hz) and an improvement ingait and mobility.

The user may select target anatomical structures 116 to view a list ofanatomical structures that may be stimulated in order to manageParkinson's Disease, or to view a diagram illustrating the targetanatomical structures. Thus, the therapy guidelines may indicate theparticular anatomical structures 116 that should be activated by anelectrical field in order to effectively manage the patient's condition.For example, stimulating the Substantia Nigra in brain 18 may reduce thenumber and magnitude of tremors experienced by patient 12. In someexamples, the location of target anatomical structures 116 and referencetherapy fields 112 may be viewed on an anatomical reference. Forexample, upon selection of reference therapy fields 112 and/oranatomical structures 116 on GUI 110, processor 60 may display theselected reference therapy fields 112 and/or anatomical structures 116on GUI 200 (FIG. 12), 240 (FIG. 14) or 260 (FIG. 15).

FIG. 7 illustrates a schematic representation of an example GUI 130 thatmay be presented on the display of user interface 64 of programmer 20 ofFIG. 3. By interacting with GUI 130, a user may generate an algorithmicmodel of an electrical stimulation field produced by a selected therapyprogram. In some examples, the user may be able to create a stimulationfield in the field view and direct processor 60 of programmer 20 togenerate a set of therapy parameter values (e.g., a therapy program)that would best match the stimulation field. In some examples, the usermay change the size, shape or position of the stimulation field withinGUI 130 using graphical input media such as cursor or stylus control.The generated electrical stimulation field may be utilized as analgorithmic model of a therapy field associated with the generatedparameters. More particularly, as described below, a comparison of thestimulation field model generated with the aid of GUI 120 to a referencetherapy field defined by therapy guidelines and/or analysis of theefficiency of therapy system 10 may be used to modify the therapyparameter values.

GUI 130 illustrates lead 16, which includes a complex electrode arraygeometry. A complex electrode array geometry generally refers to anarrangement of stimulation electrodes at multiple non-planar ornon-coaxial positions, in contrast to simple electrode array geometriesin which the electrodes share a common plane or a common axis. Anexample of a simple electrode array geometry is an array of ringelectrodes distributed at different axial positions along the length ofa lead comprising a circular cross-section. This type of electrode arraygeometry is shown in FIG. 2. Another example of a simple electrode arraygeometry is a planar array of electrodes on a paddle lead.

In the example of FIG. 7, rather than including four electrodes 17 asshown in FIG. 1A, lead 16 includes four electrode “levels” at differentaxial positions along the length of the lead. Each level includes fourelectrodes generally arranged in a ring. However, the electrodes arenon-contiguous with one another. The electrodes may be referred to assegmented electrodes or electrode segments. Each electrode is coupled toa respective electrical conductor within lead 16. Hence, lead 16includes multiple electrical conductors, e.g., wires, cables or thelike, that extend from the proximal end of the lead to respectiveelectrodes to electrically couple the electrodes to electrical terminalsassociated with IMD 14.

Each electrode is positioned at a different angular position around thecircumference of implantable lead 16, which has a generally circularcross-section in the example of FIG. 7. Each electrode is independentlyselectable so that stimulation energy can be delivered from the lead atdifferent axial and angular positions. In some examples, lead 16 mayinclude combinations of complex electrode array geometries and simpleelectrode array geometries. For example, ring electrodes that extendabout the entire circumference of the lead may be used in combinationwith electrodes disposed at different axial and angular positions.Selective activation of the electrodes carried by lead 16 can producecustomizable stimulation fields that may be directed to a particularside of lead 16 in order to isolate the stimulation field around atarget anatomical region of brain 18.

GUI 130 illustrates a side view 131 and multiple cross-sectional views132A-132D of lead 16 in alignment with corresponding electrode levels.In the example shown in FIG. 7, the user has selected an initialelectrode combination, either manually or by selection from a set ofelectrode combinations provided by programmer 20, and the selectedelectrode combination is illustrated in GUI 130. GUI 130 presents arepresentation of a stimulation field 134 defined by the user andproduced by the selected electrode combination, given stimulationparameter values selected by the user and general tissue characteristicsstored within programmer 20. The general tissue characteristics mayinclude, for example, impedance of tissue proximate to the electrodes oflead 16. Stimulation field 134 may represent an algorithmic model of atherapy field.

The size and shape of stimulation field 134 may be established based ongeneric physical characteristics of human tissue and known physicalcharacteristics of the electrodes of lead 16. In other words,stimulation field 134 displayed in GUI 130 may only be an approximationof what the stimulation field would be in brain 18 of a specific patient12. However, in some examples, physical characteristics of the actualanatomical structure of patient 12 being treated may be used to generatestimulation field 134. This anatomical structure information may bepresented to programmer 20 in the form of patient anatomical datagenerated by an imaging modality, such as CT, MRI, or any othervolumetric imaging system and stored within memory 62 (FIG. 3). In theexample that uses the patient anatomical data, stimulation field 134 maybe similar to an electrical field model, which is discussed in detailwith reference to FIGS. 8 and 10. For example, stimulation field 134 mayrely on tissue impedance models, field propagation models, and the like.In some examples, stimulation field 134 may be a representation of anelectrical field, current density, voltage gradient, or neuronactivation, applied to a generic human tissue or the anatomy of patient12. In addition, the user may be able to switch between any of theserepresentations when desired.

The user may move stimulation field 134 up or down relative to alongitudinal axis of lead 16 using vertical scroll bar 136 or somesimilar control interface. As stimulation field 134 moves up or down inresponse to the user input, programmer 20 automatically selectsappropriate electrode combinations to support the vertical movement ofstimulation field 134 within GUI 130. For example, processor 60 mayphase electrodes in and out as stimulation field 134 travels upward ordownward, reducing the stimulation energy delivered from some electrodesas the stimulation field moves away from them, and increasing thestimulation energy delivered by other electrodes as the field movestoward them. Also, GUI 130 includes arrows 138 or similar input mediathat permit the user to transition between different electrode levels ofthe lead in cross-sectional views 132A-132D.

In addition, the user may rotate stimulation field 134 using horizontalscroll bar 140 or some similar control device. An arrow 142 may beprovided next to horizontal scroll bar 140 to indicate the orientationof lead 16 relative to an anatomical structure. In addition, arrows maybe provided in respective cross-section views 132A-132D to maintainorientation. As the user rotates stimulation field 134, processor 60 ofprogrammer 20 may automatically select appropriate electrodecombinations to support the rotational movement of the stimulation field134. As in the case of vertical movement, rotational movement ofstimulation field 134 may be accomplished by gradually reducing thestimulation energy delivered to some electrodes as the stimulation fieldrotates away from them, and gradually increasing the stimulation energydelivered to other electrodes as the stimulation field rotates towardthem. Side view 131 and cross-sectional views 132A-132D permit the userto observe movement of stimulation field 134 from both an axialperspective and a rotational perspective.

Movement of stimulation field 134 within GUI 130 using scroll bars 136,140 or similar input media permits the user to evaluate differentstimulation field positions without the need to manually selectelectrodes and manually enter parameter values. Instead, processor 60 ofprogrammer 20 automatically selects electrodes and parameter values inresponse to movement of stimulation field 134 by the user. Althoughscroll bars 136, 140 are illustrated as examples of input media formovement of stimulation field 134, other types of input media may beused. Examples include up/down arrows or side-to-side arrows, which maybe presented on a touch screen or formed by buttons or keys onprogrammer 20.

As a further alternative to manipulating the stimulation field 134, theuser may select stimulation field 134 with a stylus, mouse, or otherpointing device and drag the field upward, downward, or rotationally. Insome examples, a mouse or other pointing device may support left orright click functionality to perform different operations relative tostimulation field 134. With a stylus, a first click on stimulation field134 may initiate movement, dragging with the stylus directs movementrelative to the schematic illustration of lead 16 in GUI 130, and asecond click may terminate movement. In each case, processor 60 ofprogrammer 20 responds to the specified movement by automaticallyadjusting the electrode combination and the stimulation parameters toapproximate the characteristics of stimulation field 134 presented byGUI 130. As the stimulation parameter values change, the size and shapeof stimulation field 134 presented on the display change. Similarly, asthe electrode combination changes in terms of polarity or electrodeselection, the size, shape or direction of stimulation field 134presented on the display changes.

In some examples, processor 60 of programmer 20 may utilize stimulationtemplates and select the best fitting stimulation template set to anewly modified stimulation field 134 in order to generate therapyparameter values for achieving stimulation field 134. A stimulationtemplate is a predetermined volumetric stimulation field that processor60 of programmer 20 may substantially match to a desired stimulationfield 134 from the user. An algorithm for generating stimulationparameter values that fit the user defined stimulation field may be lesscomputationally intensive for processor 60 compared to an algorithm thatreferences multiple equations or lookup tables to generate thestimulation parameters. The stimulation template may be a representationof an electrical field or other electrical stimulation relatedcharacteristic, e.g., current density, voltage gradient, or neuronactivation, applied to a generic human tissue. For stored stimulationtemplates, processor 60 may adjust the current amplitude or voltageamplitude to alter the size of the stimulation template to cover thedesired stimulation field 134 from the user. Examples of stimulationtemplates are described in U.S. Patent Application Publication No.2007/0203541 by Goetz et al.

Processor 60 of programmer 20 may limit the rate of movement ofstimulation field 134 within GUI 130. In other words, stimulation field134 may only be moved a certain number of steps per second within GUI130, or any other user interface that allows the user to drag thestimulation field. This rate movement limit may prevent unnecessarycalculations or ensure patient comfort in real-time programmingexamples.

In addition to moving stimulation field 134, GUI 130 may permit the userto perform one or more operations that result in reconfiguration ofstimulation field 134. For example, the user may click on a border,i.e., an outer perimeter, of stimulation field 134, and drag it inwardor outward to resize the stimulation field. Resizing by enlarging orshrinking stimulation field 134 in GUI 130 may result in an increase ordecrease in amplitude, pulse width or pulse rate values of the therapyprogram used to generate stimulation field 134. In some examples,enlarging or shrinking stimulation field 134 also may result inselection or de-selection of electrodes included in the existingelectrode combination. In either case, processor 60 of programmer 20adjusts the electrode combination and/or parameter values in response tothe enlargement or shrinkage of stimulation field 134 by the user.

When a user clicks on stimulation field 134 border and drags it, theentire stimulation field may be expanded in two dimensions in equalproportions. Alternatively, stimulation field 134 may expand only in thedirection in which the user drags the stimulation field. For example,horizontal dragging of the field perimeter to enlarge stimulation field134 may result in overall enlargement of the cross-sectional seize ofstimulation field 134, keeping the vertical to horizontal aspect ratioconstant. Alternatively, horizontal dragging may result only inhorizontal expansion, leaving the vertical dimension constant. Theapplication of a constant or varying aspect ratio may be specified by auser as a user preference. Alternatively, programmer 20 may providedifferent aspect ratio modes on a selective basis for expansion andshrinkage of stimulation field 134.

To enlarge or shrink stimulation field 134, the user may simply click onthe stimulation field border within GUI 130. Alternatively, the user mayclick on a grow/shrink button 144 as shown in FIG. 7, and then click onthe border of stimulation field 134 to drag it inward or outward andthereby adjust the size of the stimulation field. In response, processor60 of programmer 20 may automatically reconfigure the electrodecombination and/or stimulation parameter values to approximate theresized stimulation field. In this way, a user may generate analgorithmic model of a therapy field by directly manipulating thestimulation field 134. Other field adjustment functions such asspread/focus button 146 and split/merge button 148 may be provided byGUI 130. In each case, the user changes stimulation field 134 by simplychanging the representation of the stimulation field 134 presented onGUI 130, thereby avoiding the need to manually select electrodes andparameter values. The operation of the buttons 144, 146, and 148 isdescribed in further detail in U.S. Patent Application Publication No.2007/0203541 by Goetz et al.

After selecting a desirable stimulation field 134, processor 60 ofprogrammer 20 may generate an algorithmic model of an electrical fieldand/or an algorithmic model of an activation field that corresponds tostimulation field 134. Techniques for generating algorithmic models ofelectrical fields and activation fields are described with reference toFIGS. 8-11. The model of the electrical field and/or the model of theactivation field may be utilized as the algorithmic model of a therapyfield associated with the set of therapy parameter values that generatestimulation field 134. As previously discussed, the algorithmic model ofthe therapy field may be useful for guiding the modification of therapyparameter values. In accordance with example techniques described abovewith respect to FIGS. 4A-4C, for example, the therapy parameter valuesare based on a comparison of the therapy field model to a referencetherapy field defined by therapy guidelines and/or analysis of theefficiency of therapy system 10.

In FIG. 7, processor 60 of programmer 20 may display reference field 149in addition to the electrical field model and/or activation field modelon GUI 130. For example, reference field 149 may be displayedconcurrently with the stimulation field 134 or a user may be permittedto toggle between views of stimulation field 134 and reference field149. In some examples, a user may select which type of therapy fieldmodels (e.g., stimulation field, activation field or electrical field)and/or reference fields GUI 130 displays. Reference field 149 may beprovided as part of therapy guidelines (FIGS. 6A-6C), and may include anelectrical field or an activation field that is known or believed, bythe clinician, to manage the patient's condition (e.g., based on one ormore other patients and their respective responses to therapy deliveryvia a therapy field that resembles the reference field), and may bestored within memory 62 of programmer 20. The user may select therapyguidelines with the aid of programmer 20, as previously described withreference to FIGS. 6A-6C.

As described previously, processor 60 may facilitate comparison of theelectrical field model or activation field model to reference field 149.Processor 60 may also adjust the stimulation parameter values of atherapy program based on the comparison. In the example shown in FIG. 7,stimulation field 134 has a greater volume than reference field 149.Processor 60 may calculate the ratio of the volume of reference therapyfield 149 to the volume of stimulation field 134. Additionally oralternatively, processor 60 may analyze the percentage of overlapbetween reference field 149 and stimulation field 134 and/or the volumeof stimulation field 134 that falls outside of reference field 149.Based on its comparison, processor 60 may adjust one or more stimulationparameter values of the therapy program on which stimulation field 134is based, e.g., to decrease the size and/or position of stimulationfield 134. GUI 130 may display one or more therapy field models and/orstimulation fields associated with the adjusted set of stimulationparameters.

Processor 60 of programmer 20 may also analyze the power efficiency oftherapy system 10 when IMD 14 delivers stimulation according to thetherapy program selected by processor 60. For example, processor 60 mayadjust the stimulation parameter values of the therapy program based onoperating efficiency data in order to increase the operation efficiencyof therapy system, 10 while substantially maintaining at least onecharacteristic of stimulation field 134, such as volume or centroid ofstimulation. In some examples, processor 60 may generate an algorithmicmodel of therapy field based on the adjusted set of stimulationparameter values, and GUI 130 may display the therapy field model inaddition to or instead of stimulation field 134 and/or reference field149, to verify that the at least one characteristic of the therapy fieldis substantially maintained.

FIGS. 8 and 9 are schematic diagrams illustrating example GUIs 150, 152that present electrical field models and activation field models,respectively, to a user. FIG. 8 illustrates an example GUI 150 thatdisplays a stimulation field view to the user via the display ofprogrammer 20. GUI 150 displays side view 154 and cross-sectional view156 of implanted lead 16, and the user defines stimulation field 158 onthe side and cross-sectional views, e.g., using the techniques describedabove with respect to FIG. 7. Processor 60 of programmer 20 may generatea therapy program for therapy based on the selected stimulation field158 and generate an electrical field model 160, which estimates anelectrical field that results from therapy delivery according to thestimulation parameters associated with the selected stimulation field158. In GUI 150, electrical field model 160 is displayed as anelectrical field within the outer boundaries of stimulation field 158.In other examples electrical field model 160 may be a representation ofanother electrical stimulation related characteristic, e.g., currentdensity, or voltage gradient. In addition, the user may be able toswitch between any of these representations when desired.

Electrical field model 160 represents where the electrical current willpropagate from the implanted lead 16 within tissue of patient 12, astissue variation within patient 12 at the target tissue site may changethe electrical current propagation from the lead in some directions. Thevariations in electrical field propagation may affect the ability of thetherapy to actually treat a desired structure of brain 18 in examples inwhich IMD 14 delivers stimulation to brain 18 (FIG. 1A) or cause aside-effect. The horizontal and axial views of electrical field model160 illustrated in FIG. 8 are 2D slices of a volumetric electrical fieldmodel generated by processor 60 of programmer 20. Processor 60 utilizesan algorithm to generate electrical field model 160. In one example, thealgorithm considers the patient anatomy data and electrical field modelequations that define electrical current propagation. Accordingly, ifthe algorithmic model of the therapy field includes electrical field160, processor 60 may implement an algorithm that applies electricalfield model equations that define how the electrical field propagatesaway from an origin location. The electrical field model equations maybe specific to patient 12. The electrical field equations require thephysical tissue characteristics of the tissue adjacent lead 16, which isincluded in the patient anatomy data set. From this information,processor 60 is able to generate the estimated electrical field 160 thatwill be produced in therapy.

Electrical field 160 may differ from the selected stimulation field 158because processor 60 generates stimulation field 158 using an algorithmthat only considers general tissue characteristics, which are notspecific to patient 12. In other examples, the electrical fieldequations may utilize matrices or other mathematical model of theelectrical field. In this manner, electrical field 160 can be estimatedand modeled for the user. Accordingly, the user may be able to increaseor decrease the amplitude of the stimulation parameters with anamplitude interface 162 in order to change the size and possibly shapeof electrical field 160 or directly manipulate electrical field 160.

Once the user is satisfied with electrical field 160, processor 60 maycompare electrical field model 160 to a reference field (e.g., referencefield 149 in FIG. 7) defined by therapy guidelines as described withrespect to FIGS. 4A-4C, and/or analyze the efficiency of therapy system10 based on the stimulation parameter values used to generate electricalfield model 160, as describe with respect to FIG. 5. In some examples,GUI 150 may display the reference therapy field specified by the therapyguidelines selected by the user, and/or an electrical field modelassociated with the modified therapy program that resulted from thecomparison to the reference field. In examples in which processor 60adjusts the stimulation parameter values to increase the operationefficiency of therapy system 10 while substantially maintaining theelectrical field, GUI 150 may display a model of the electrical fieldassociated with the adjusted parameters to allow the user to verify thatthe therapy field is substantially maintained.

FIG. 9 is similar to FIG. 8 and illustrates an example GUI 152 thatdisplays an activation field view to the user via the display ofprogrammer 20. From the defined stimulation field 158 on the side view154 and cross-sectional view 156, processor 60 of programmer 20 maygenerate stimulation parameter values for therapy and generate anactivation field model based upon the electrical field model 160 of FIG.8 and a neuron model that estimates which neurons within the electricalfield model will be activated by the voltage of the electrical fieldduring therapy. The neuron model may be a set of equations, a lookuptable, or another type of model that defines threshold action potentialsof particular neurons that make up the anatomical structure, as definedby the patient anatomy data, affected by the electrical field 160. Ifthe voltage or current amplitude of the electrical field 160 is abovethe threshold of any neuron within the electrical field, that neuronwill be activated, e.g., cause a nerve impulse. The activation fieldmodel is displayed as activation fields 166 and 168 within stimulationfield 158.

Activation fields 166 and 168 of the activation field model indicate tothe user where neurons around the lead will be activated from thestimulation therapy. Due to changes in electrical current propagationand voltage thresholds to activate a neuron, the activation of neuronsmay vary with the location of tissue around the lead. Some neurons mayactivate further from the lead with smaller voltages while other neuronsmay only be activated close to the lead because of a high voltagethreshold. These differences in neurons may account for separateactivation fields 166 and 168 within a contiguous stimulation field 158.The user may manipulate activation fields 166, 168 in order to modifythe therapy program that resulted in stimulation field 158. For example,the user may increase or decrease the size and/or shape of activationfields 166 and 168 by changing the amplitude with amplitude adjustmentinterface 162 or directly manipulate the activation fields (e.g., bymodifying the borders of the displayed activation fields 166, 168) toautomatically modify the stimulation parameters. In both GUI 150 (FIG.8) and GUI 152 (FIG. 9), the user may view cross-sections at otherelectrode levels with arrows 138.

Once the user is satisfied with activation fields 166, 168, processor 60may compare activation fields 166, 168 to a reference field (e.g., areference activation field) defined by a set of therapy guidelines, asdescribed with respect to FIGS. 4A-4C, and/or analyze the efficiency oftherapy system 10 based on the stimulation parameters used to generateactivation fields 166, 168, as described with respect to FIG. 5. Forexample, processor 60 may access a set of therapy guidelines and selecta reference therapy field, e.g., via memory 62 or a separate computingdevice, and compare the reference therapy field to activation fields166, 166. Additionally or alternatively, processor 60 may analyze theefficiency of therapy system 10 when the selected the stimulationparameters are used to generate activation fields 166 and 168. In someexamples, GUI 152 may display the reference field defined by the therapyguidelines, an activation field model associated with the adjustedstimulation parameters that resulted from the comparison to thereference field, and/or a model of the electrical field associated withthe adjusted stimulation parameters that resulted from the analysis ofthe efficiency of therapy system 10.

GUIs 150, 152 also include scroll bars 136, 140, which are describedwith respect to FIG. 7. In the example shown in FIGS. 8 and 9, GUIs 150,152 also present field menu button 172 to the user, which may presentfurther options to a user. For example, upon activation of menu button172, the GUIs 150, 152 may display a menu that enables a user to selecta modify stimulation field button to redefine the stimulation field 158,select polarity button to alter the polarity of any of the electrodes, achange field view button to switch between electrical or activationfield views 150, 152, and a manual mode button which allows the user tomanually select the stimulation parameters in an electrode view thatdisplays the electrodes of the lead.

Although FIGS. 8 and 9 illustrate 2D views of lead 16, in otherexamples, a user interface may present a 3D view of lead 16 and theassociated electrical field and activation fields may be displayedrelative to the 3D views of lead 16.

FIG. 10 is a flow diagram illustrating an example technique forcalculating and displaying electrical field model 160 (FIG. 8), which isbased on a stimulation field 158. Stimulation field 158 may bedetermined based on input by a user and/or automatically generated byprocessor 60 of programmer 20 in response to a therapy program selectedby the user. As shown in FIG. 10, processor 60 receives patient anatomydata necessary for creating an electrical field (180), which may includean anatomical image of the target tissue site of patient 12, a referenceanatomical image, which may not be specific to patient 12, an anatomicalatlas indicating specific structures of the patient's anatomy or a mapof the tissue characteristics (e.g., conductivity or density) adjacentto lead 16. As previously described, the patient anatomy data may becreated based on a medical imaging technique, such as, but not limitedto, CT and MRI data. Processor 60 may store the patient anatomy datawithin memory 62 (FIG. 3).

Processor 60 may enter the patient anatomy data into stored electricalfield model equations or equation sets to satisfy anatomical variable(182). Processor 60 may then determine the electrical field model fromthe data and equations (184). Once processor 60 receives stimulationinput from a user defining the stimulation field, e.g., via userinterface 64 (186), the modeled electrical field (algorithmic model) maybe displayed to the user via the display of user interface 64 (188).Processor 60 may also compare the algorithmic model of the electricalfield to a reference electrical field defined by a set of therapyguidelines, as described with respect to FIGS. 4A-4C, and/or analyze theefficiency of therapy system 10 using the stimulation parameters onwhich the modeled electrical field is based, as described with respectto FIG. 5.

FIG. 11 is a flow diagram illustrating an example technique fordetermining and displaying the activation field model of definedstimulation. As shown in FIG. 11, processor 60 receives patient anatomydata indicative of the anatomy of patient 12 (180) and processor 60determines the electrical field model from the patient anatomy data(184). Processor 60 retrieves a neuron model from memory 62 (FIG. 3) andfits the neuron model to the electrical field model (192). The neuronmodel may be stored within of memory 62 (FIG. 3). Processor 60 maydetermine the activation field model based upon the electrical fieldmodel and neuron model (194).

Processor 60 may receive input from a user defining stimulation field158, e.g., via user interface 64 (186). Processor 60 may present theresulting activation field model to the user via the display of userinterface 64 (196). Processor 60 may also compare the algorithmic modelof the activation field to a reference activation field defined by a setof therapy guidelines, as described with respect to FIGS. 4A-4C, and/orevaluate the efficiency of therapy system 10 based on the set ofstimulation parameters used to generate the stimulation field, asdescribed with respect to FIG. 5.

The techniques shown in FIGS. 10 and 11 may also be used to generate analgorithmic model of a modified therapy field based on the modifiedtherapy program, e.g., a therapy program that was modified based oncomparison to a reference therapy field defined by therapy guidelinesand/or modified to increase an operating efficiency of therapy system10. If the algorithmic model of the modified therapy field is anelectrical field model, processor 60 may receive patient anatomy data(180), enter the patient anatomy data and the modified therapy programdata into electrical field model equations (182), and determine analgorithmic model of an electrical field that is based on the modifiedtherapy program (184) (FIG. 10). If the algorithmic model of themodified therapy field is an activation field model, processor 60 mayreceive patient anatomy data (180), enter the patient anatomy data andthe modified therapy program data into electrical field model equations(182), determine the electrical field model based on the equations(184), and retrieve a neuron model and fit it to the electrical fieldmodel (192) in order to determine an activation field model based on themodified therapy program (194) (FIG. 11).

An algorithmic model of an original therapy field (e.g., a therapy fieldprior to modification of the therapy parameter values based on areference therapy field and/or operating efficiency data of the therapysystem), a modified therapy field or another algorithmic model of atherapy field may also be generated using other techniques. FIG. 12 is aschematic illustration of another example of GUI 200 that may bepresented on the display of programmer 20 in order to help a usergenerate an algorithmic model of a therapy field, compare thealgorithmic model to a reference therapy field, and/or modify a therapyprogram to increase the operating efficiency of therapy system 10.

A user may interact with GUI 200 via user interface 64 of programmer 20in order to generate an electrical field model and/or an activationfield model. GUI 200 presents a representation of anatomical regions ofbrain 18. In GUI 200, a lead icon 202 representing lead 16 is displayedto illustrate where lead 16 is actually implanted relative to one ormore anatomical regions of brain 18 of patient 12. In particular, GUI200 displays coronal view 204 of brain 18, which is a front-backvertical section of brain 18. Coronal view 204 may be an actual image ofbrain 18 produced with MRI, CT, or another imaging modality. Theseimages are used to produce the anatomical regions needed to help theuser program the stimulation parameters.

Coronal view 204 is a 2D coronal slice of brain 18. Differently shadedportions of coronal view 204 indicate varying densities of tissue withinbrain 18. Darker portions indicate less dense tissue. For example, thedarkest portion of coronal view 204 is indicative of spaces within brain18 that contain cerebral spinal fluid (CSF). White portions of brain 18indicate dense tissue and more neurons. The clinician may be able torecognize target anatomical regions by viewing coronal view 204. Itshould be noted that coronal view 204 shown in FIG. 12 is merely anexample image, and actual images may include a wider range of shades andhigher image resolution. Coronal view 204 provides a first perspectiveof the lead and the anatomical region in which the lead is implanted.

Coronal view 204 further includes pointer 206, previous arrow 208, nextarrow 210, stimulation field 212, fine control input mechanism 214, andcontrol slide 216. Pointer 206 may be controlled with a mouse andbuttons, a track-ball, touch-pad, touch screen or other movement inputdevice, which may be a part of user interface 64 of programmer 20. Auser may use pointer 206 to drag lead icon 202 into position or rotatelead icon 202 within coronal view 204 to correctly orient the lead iconaccording to the actual position of lead 16 within brain 18. The actualposition of lead 16 may be determined with the aid of medical imagingtechniques, such as MRI or CT. In other examples, the user may firstselect the type of lead 16 implanted within patient 12 and select thecorrectly scaled size of lead icon 202 to correspond with the anatomicalregions of coronal view 204.

Programmer 20 may initially orient the user to the middle depth of thecoronal view 204 or another depth that the programmer automaticallyselects based upon the type of therapy, implant location, or some othersimple indication of location. However, the user may use arrows 208 and210 to move to another coronal depth where lead 16 is implanted in brain18. The clinician may zoom in to or out of coronal view 204 for a largerview of anatomical regions of the coronal view. In addition, theclinician may move coronal view 204 up, down, left, or right to view alarger or smaller portion of brain 18. While the clinician may manuallyposition lead icon 202 within coronal view 204, processor 60 mayautomatically position lead icon 202 within GUI 200 based uponstereotactic data that is generated before lead 16 is implanted withinpatient 12. A stereotactic frame may be placed on a cranium of patient12 to specifically locate areas of brain 18. In addition, thisstereotactic information may be used to provide coordinates of the exactlocation of the implanted lead 16. In other examples, brain 18 may beimaged after implantation of lead 16 such that the lead is identifiableon coronal view 204. The user may point to and identify electrodes oflead 16 in the image to allow programmer 20 to reconstruct the correctposition of the lead 16. In some cases, programmer 20 may automaticallyidentify lead 16 and place lead icon 202 correctly within the anatomicalregion without any input from the user.

GUI 200 allows the user to select and adjust stimulation field 212,which is a cross-sectional view of volumetric stimulation field, whichmay be further defined in other orthogonal views. In order to definestimulation field 212 within coronal view 204, the user may user pointer206 to select one of electrode levels 218A, 218B, 218C or 218D fordelivering the stimulation that results in stimulation field 212. Aswith the lead shown in FIGS. 8 and 9, an electrode level may have one ormore electrodes around the circumference of lead icon 202, e.g., acomplex electrode array geometry. All circumferential electrodes of theselected electrode level are initially activated for programming. Insome cases, the user may attempt to place stimulation field 212 over theanatomical regions targeted for stimulation therapy while avoidinganatomical regions that may initiate unwanted side effects. In someexamples, stimulation field 212 may be a representation of an electricalfield, current density, voltage gradient, or neuron activation, appliedto a generic human tissue or the anatomy of patient 12. In addition, theclinician may be able to switch between any of these representationswhen desired.

In the example shown in FIG. 12, the user-selected electrode level 218Cand stimulation field 212 shows the anatomical region that would bestimulated with therapy delivery via the selected electrode level 218C.The user may use pointer 206 to drag stimulation field 212 to define asmaller or larger size, which corresponds to a lower or higher voltageor current amplitude. For example, the user may click on a border, orperimeter of stimulation field 212, and then drag the border to expandor contract the field 212. This adjustment is the coarse control of thesize of stimulation field 212. The clinician may use pointer 206 to movecontrol slide 216 up to slightly increase the size of stimulation field212 or down to slightly decrease the size of stimulation field 212. Insome examples, the actual voltage or current amplitude associated withstimulation field 212 is displayed on coronal view 204 as stimulationfield 212 changes characteristics.

Processor 60 of programmer 20 may limit the rate of movement ofstimulation field 212. In other words, stimulation field 212 may only bemoved a certain number of steps per second within GUI 200, or any otheruser interface that allows the clinician to drag the stimulation field.This rate movement limit may prevent unnecessary calculations or ensurepatient comfort in real-time changing of stimulation parameters withmodifications of stimulation field 212.

The initial size of stimulation field 212 may be determined by a minimalthreshold voltage previously determined to provide some efficaciousresults to patient 12. In other examples, the initial stimulation fieldsize may be small to allow the clinician to safely increase the size ofstimulation field 212. The size of stimulation field 212 may be limitedby a volume parameter or a maximum voltage limit previously defined bythe user or processor 60. The limit may be associated with capabilitiesof IMD 14 or safe voltage or current levels for patient 12. Once thesize of stimulation field 212 is met, the clinician may no longer beable to drag the size of the stimulation field away from lead icon 202.

Stimulation field 212 may grow in size or split if the clinician selectsmore than one electrode level 218A-218D. For example, the clinician mayselect electrode levels 218A and 218B to generate stimulation fieldsassociated with each electrode level. The clinician may also movestimulation field 212 along the length of lead icon 202 and processor 60may automatically select which electrode levels to activate to producethe stimulation field 212. The clinician may also move to other depthsor slices of coronal view 204 with arrows 208 and 210. View button 141may permit a user to switch to another view of brain 18. The other viewsmay include, for example, a sagittal view of brain tissue, which may betaken from a perspective substantially perpendicular to the coronal view204 or an axial view.

As described in further detail in U.S. patent application Ser. No.11/591,299 to Stone et al., a programmer 20 may present a GUI includingother views of brain 18 in addition to or instead of coronal view 240 inorder to help select stimulation parameters for IMD 14. For example,programmer 20 may present a sagittal view of brain tissue or an axialview of brain tissue.

FIG. 13 is a flow diagram illustrating an example technique foradjusting stimulation field 212 for stimulation therapy in order todefine stimulation parameter values and generate a therapy program fortherapy delivery by IMD 14 and to generate an algorithmic model of atherapy field. As shown in FIG. 13, the clinician begins by selecting anelectrode level 218A-218D in coronal view 204 of GUI 200, although otherviews, such as a sagittal view or axial view of brain 18 may also beused to select an electrode level 218A-218D (220). Processor 60activates all the electrodes, i.e., electrodes at different angularpositions around the lead circumference, in the selected electrodelevel. The user may interact with GUI 200 in order to adjust a size ofstimulation field 212 (222) and test the stimulation field 212 onpatient 12 to determine the therapeutic efficacy, if any (224). If theuser wants to test stimulation delivered by more electrode levels (226),the user may repeat this process by selecting another electrode leveland testing it on patient 12.

If there are no more electrode levels to test, the user may select themost effective electrode level from the tested electrodes (228) andadjust the size of stimulation field 212 by interacting with GUI 200(230). The user may drag stimulation field 212 within GUI 200 in orderto define a field 212 that minimizes side effects and maximizestherapeutic benefits to patient 12 (232). In addition, the user may usefine adjustment buttons 214 and 216 to further adjust stimulation field212 (234). Additionally, the clinician may use a wand tool to select arange of pixel shades to quickly select anatomical regions that will beincluded in stimulation field 212.

In some examples, the user may adjust the stimulation field in any ofsagittal, coronal, or axial field views as desired by the clinician. Inother examples, GUI 200 may require that the clinician enters each ofthe sagittal, coronal, and axial field views at least once beforeadjustment of the stimulation can be completed. Processor 60 ofprogrammer 20 may use information received via user interface 64 toautomatically generate stimulation parameter values based on thestimulation field 212 defined by the user. Processor 60 may determinethe dimensions of the stimulation field 212 to create a 3D vector fieldidentifying the distances from lead 16 that stimulation may reach.Processor 60 may utilize the 3D vector field with an equationapproximating electrical current propagation within brain tissue. Theresulting data determines respective values for the electrodecombination, voltage and current amplitudes, pulse rates, pulse widths,and, in some cases, other stimulation parameter values (e.g., slew rateor duty cycle) needed for reproducing the stimulation field withinpatient 12. In other examples, processor 60 of programmer 20 interpretsdensity of tissue in the imaging data to more precisely approximate thestimulation parameters.

In some examples, processor 60 may utilize one or more stimulationtemplates stored within memory 62 in order to determine the stimulationparameter value for achieving the stimulation field 212 defined by theuser. As previously described, a stimulation template may be apredetermined volumetric stimulation field that processor 60 may matchto a desired stimulation field 212. Each stimulation template may bebased upon any one or combination of modeled data, experimental data, oranalytical calculations prior to being stored in programmer 60.Stimulation templates are described in further detail in U.S. Pat. No.7,822,483 to Stone et al.

Once the user has indicated that stimulation field 212 is finalized, andproduces effective therapy for patient 12, processor 60 may utilizestimulation field 212 as an algorithmic model of a therapy field andmodify at least one of the stimulation parameter values based on acomparison of stimulation field 212 with a reference therapy field(FIGS. 4A-4C) (236). The stimulation parameter values that are modifiedmay be the stimulation parameter values that were determined byprocessor 60 to result in stimulation field 212 when IMD 14 deliverstherapy according to the stimulation parameter values. In anotherexample, processor 60 may utilize stimulation field 212 as analgorithmic model of a therapy field and modify the therapy programbased on an analysis of the efficiency of therapy system 10 when therapyis delivered according to the therapy program (FIG. 5) (236).

The user may save the adjusted stimulation parameters that achieve theadjusted stimulation field as a therapy program within memory 62 (FIG.3) (238). Processor 60 may control the transmission of the therapyprogram to IMD 14 via telemetry device 66 (FIG. 3). In some examples,the user may repeat the programming procedure with GUI 200 to generatemultiple therapy programs and respective algorithmic models of therapyfields. The clinician may also reprogram the therapy at any time withthe aid of GUI 200 and generate an algorithmic model of a stimulationfield based on the reprogrammed therapy program.

In other examples, a user may generate an algorithmic model of astimulation field 212 without the aid of a lead icon 202. For example,when presented with the coronal view of the brain, as shown in FIG. 12,the user may create an outline defining the outer edges of stimulationfield 212. By defining an algorithmic model of stimulation field 212 byoutlining the desired field within GUI 200, the user outlining desiredareas includes allowing the user to focus on the anatomy and physiologyof patient 12 instead of manipulating an implanted device. Consequently,automatically generating stimulation parameters according to auser-selected stimulation area may increase therapy efficacy anddecrease programming time. The user may determine the anatomy with whichto focus on with the stimulation field 212 with the aid of therapyguidelines. For example, as shown in FIG. 6C, therapy guidelines mayinclude a listing of target anatomical structures. The target anatomicalstructures specified by the therapy guidelines may be highlighted,outlined or otherwise differentiated within GUI 200, such that thetarget anatomical structures associated with the patient condition bythe therapy guidelines are easily discernible by the user.

In addition, in other examples, a user may select stimulation parametersand generate an algorithmic model of a therapy field that indicates thefield that provides efficacious therapy to patient 12 with the aid of anatlas of an anatomical region of patient 12. The atlas may berepresented in the form of a drawing or actual image from an imagingmodality such as MRI, CT, or other similar imaging technique. Thereference anatomy may be an anatomy different from patient 12 anatomy.Specific structures of the reference anatomy may be identified and theirlocations within the reference anatomy determined to create an atlas.The atlas may be stored in memory 62 of programmer 20. While an atlasmay differ from the actual patient anatomy, the structure locations maybe close enough to provide guidance to a user to generate stimulationparameters based upon the atlas. Again, the atlas may highlight, outlineor otherwise differentiate particular anatomical structures that aredefined by therapy guidelines as being relevant to treating thepatient's condition.

In addition, in some examples, the user may generate an algorithmicmodel of a therapy field with the aid of a user interface that presents,at the same time, an atlas and the actual anatomy of patient 12, e.g.,generated by a suitable medical imaging technique. The atlas of thereference anatomy and the patient-specific anatomy may be combined tocreate a morphed atlas for programming the stimulation therapy. Oneexample of how programmer 20 may create a morphed atlas is described inU.S. Patent Application No. 2005/0070781 by Dawant et al., entitled,“ELECTROPHYSIOLOGICAL ATLAS AND APPLICATIONS OF SAME” and filed Jul. 1,2004.

Examples of systems and techniques for selecting therapy parameters andgenerating a resulting stimulation field with the aid of an atlas isdescribed in further detail in U.S. Pat. No. 7,822,483 to Stone et al.In one technique described by U.S. Pat. No. 7,822,483 to Stone et al., auser may use a pointer to select a specific structure of the atlaspresented on a user interface of a programmer, and the name of thestructure may be is displayed. The programmer may generate stimulationparameters based upon the location of the one or more selectedstructures to the location of the implanted lead. In some examplesdescribed by U.S. Pat. No. 7,822,483 to Stone et al., generatingstimulation parameters may include selection of stimulation templatesand creation of a stimulation template set based on the selectedstructures. An atlas may allow a clinician to quickly select the mostappropriate structure that needs to be stimulated to treat the conditionof patient.

Just as with GUIs 150, 152, an electrical field model or an activationfield model may be generated based on a selected stimulation field 212.The electrical field model may approximate actual stimulation effectsfrom therapy. FIG. 14 is an example screen shot of a GUI 240 thatpresents a sagittal view of a patient anatomy with an algorithmic modelof an electrical field 256 of the defined stimulation therapy. Processor60 may control the display of GUI 240 on the display of programmer 20.The sagittal view of the patient anatomy may be a 2D view of any one ofan atlas, a morphed atlas, or a patient anatomical region. GUI 240 alsoincludes previous arrow 242, next arrow 244, menu 246, view indicator248, and amplitude adjuster 250 with slider 252. The clinician interactswith GUI using pointer 254, which may be similar to pointer 206 (FIG.12).

Processor 60 of programmer 20 controls GUI 240 to display lead icon 202and electrical field 256 to present an illustration to the clinician ofwhat the electrical field of the stimulation therapy would look likeaccording to the stimulation parameters defined by the clinician usingany of the programming techniques described herein. Electrical field 256is an algorithmic model that represents where the electrical currentwill propagate from lead 16 within brain 18, as tissue variation withinbrain 18 may change the electrical current propagation from the lead.The variations in electrical field propagation may affect the ability ofthe therapy to actually treat a desired structure or cause aside-effect.

Electrical field 256 is a 2D slice of the volumetric electrical fieldmodel created by programmer 20. Processor 60 utilizes the patientanatomical region data with electrical field model equations that definecurrent propagation. Accordingly, electrical field 256 is an algorithmicmodel of an electrical field that indicates where stimulation willpropagate from an implanted lead (represented within GUI 240 by leadicon 202). The clinician may interact with GUI 240 to increase ordecrease the amplitude of the stimulation parameters with amplitudeadjuster 250 and view how the amplitude change would affect the size andshape of electrical field 256. Amplitude adjuster 250 is an analogadjustment mechanism and may also be in the form of an adjustment knobinstead of the slider. The user may move to different depths of thesagittal view with previous arrow 242 or next arrow 244 while adjustingthe amplitude of electrical field 256 with slider 252. In some examples,GUI 240 may allow the user to redefine the stimulation field andgenerate new stimulation parameters if it is believed that electricalfield 256 is unacceptable for therapy. Algorithmic model of electricalfield 256 may be generated using a technique similar to that shown inFIG. 10.

An algorithmic model of a therapy field, such as an original therapyfield based on an original therapy program or a modified therapy fieldbased on a modified therapy program, may also be generated within a 3Denvironment. FIG. 15 is a conceptual diagram illustrating a 3Dvisualization environment including a 3D brain model for defining a 3Dstimulation field. As shown in FIG. 15, GUI 260 presents a 3Denvironment 262 that illustrates brain model 264, stimulation field 266,and virtual hand 268. Stimulation field 266 may be stored as analgorithmic model of a therapy field, where stimulation field 266 isgenerated based on patient anatomy, hardware characteristics of therapysystem 10, and the stimulation parameter values of a selected therapyprogram. However, in some cases, the stimulation parameter values may beselected to achieve stimulation field 266. Thus, in such cases,stimulation field 266 may be generated based on patient anatomy andhardware characteristics of therapy system 10. GUI 260 may be presentedby processor 60 on the display of programmer 20. Brain model 264 is a 3Danatomical region and stimulation field 266 is a 3D stimulation fielddisplayed relative to brain model 264. A user may interact with GUI 200to move hand 268 in order to control the view and aspects of 3Denvironment 262. In the example shown in FIG. 15, brain model 264 ispositioned to illustrate a sagittal view.

3D environment 262 may be displayed on a 2D display by using partiallytransparent surfaces and grey or color shades. A fully interactive 3Denvironment 262 may allow a clinician to view within brain model 264 andidentify anatomical regions that are targets for stimulation therapy.Brain model 264 may be generated from imaging data from MRI, CT, oranother medical imaging modality. While shading of brain model 264 isnot shown in FIG. 15, brain model 264 may include shading or othertechniques for illustrating different anatomical regions of brain 18.

While a lead icon representing lead 16 is not shown within 3Denvironment 262, processor 60 may incorporate imaging data into 3Denvironment 262 after lead 16 is implanted. That is, processor 60 mayautomatically recognize the orientation and location of lead 16 withinpatient 12 based on imaging data input into programmer 20, and maypresent a lead icon within GUI 260 based on the actual orientation andlocation of lead 16 within patient 12. Alternatively, the user maymanually place a lead icon within 3D environment 262 based uponstereotactic data or implant coordinates for the actual lead 16implanted within patient 12.

Processor 60 may control the presentation of GUI 260 and select thelocation of stimulation field 266 based upon the implant site of lead 16within patient 12. A user may then interact with GUI 260 to adjust andmanipulate stimulation field 266 as desired with virtual hand 268 orother input mechanisms provided by user interface 64 of programmer 20(FIG. 3). The user may also use virtual hand 268 to rotate and spinbrain model 264 in any direction. GUI 260 may support zooming in and outrelative to brain model 264, as well as displaying differentperspectives of brain model 264 within 3D environment 262 to seestimulation field 266 within brain model 264 from differentperspectives.

GUI 260 may include a wand tool that allows the user to highlightvarious regions of brain model 264 to be included in stimulation field266. The wand tool may automatically select voxels (i.e., pixels in allthree dimensions). In other dimensions, the clinician may grab one ofseveral predefined stimulation field shapes and place the shape withinbrain model 264 to become stimulation field 266. In any case, GUI 260may set limits to stimulation field 266 based upon the characteristicsof lead 16 and the capabilities of IMD 14. The safety of patient 12 mayalso govern the size and location of stimulation field 266.

FIG. 16 is a flow diagram illustrating an example technique for defininga 3D stimulation field within a 3D brain model of patient 12. As shownin FIG. 16, a user, such as a clinician, may implant lead 16 withinbrain 18 using any suitable technique, such as a stereotactic technique(270). The clinician, with the aid of an imaging device, may generate animage the head of patient 12 to obtain data of brain 18 necessary forgenerating the brain model 264 (272). The clinician may upload the imagedata to a computing device, such as programmer 20 (274). The image datamay be stored within memory 62 (FIG. 3). Processor 60 of programmer 20may generate a 3D visualization environment (276) and generate brainmodel 264 and the initial stimulation field 266 within the 3Denvironment (278). The initial stimulation field may be generated with aset of stimulation parameter values that are believed to provideefficacious therapy to patient 12 for the particular patient condition.These initial stimulation parameter values may be specific to patient 12or may be general to more than one patient. For example, in one example,the initial stimulation parameter values may be specified by a set oftherapy guidelines stored within memory 62 of programmer 20.

With the aid of user interface 64, processor 60 may receive stimulationfield input from a clinician, such as adjustments and manipulations tostimulation field 266 within the 3D environment (280). Processor 60 maygenerate stimulation parameter values based on the stimulation field 266resulting form the adjustments and manipulations from the user (282) andcontrol IMD 14 to deliver test stimulation with the parameters (286). Ifthe clinician desires to adjust stimulation parameters (284) based onthe feedback from patient 12 and/or sensors, processor 60 may continuereceiving stimulation field input (280) and testing the stimulationaccording to the modification to stimulation field 266 (282, 286). Ifthe stimulation therapy is effective, processor 60 may utilizestimulation field 266 as an algorithmic model of a therapy field andadjust the stimulation parameter values based on stimulation field 266(236). For example, processor 60 may compare stimulation field 266 to areference electrical field defined by therapy guidelines and/or analyzethe efficiency of therapy system 10 using the set of stimulationparameter values that are used to generate stimulation field 266 (288).The clinician may save the adjusted stimulation parameter values as atherapy program in IMD 14 so that patient 12 can receive therapy withthe set of adjusted stimulation parameter values (290).

In addition to or instead of using stimulation field 266 as analgorithmic model of a therapy field, such as an original therapy fieldor a modified therapy field, an electrical field model and/or activationmodel may be generated based on stimulation field 266 and stored as analgorithmic model of a therapy field. The electrical field model andactivation field model may be generated by processor 60 using anysuitable technique, such as the techniques shown in FIGS. 10 and 11, anddisplayed within 3D environment 262 using any suitable technique, suchas those described in U.S. Pat. No. 7,822,483 to Stone et al. Theclinician or other user may modify the stimulation parameters bydirectly modifying the size, shape or location of the electrical fieldmodel or activation field model within 3D environment 262, or theclinician may modify the electrical field model or activation fieldmodel may directly modifying the stimulation parameters.

While the description primarily refers to electrical stimulationtherapy, in some cases, an algorithmic model of a therapy fieldresulting from the delivery of a therapeutic agent to a target tissuesite within patient 12 may be used to guide the modification of therapyparameters. In the case of therapeutic agent delivery, the therapyparameters may include the dosage of the therapeutic agent (e.g., abolus size or concentration), the rate of delivery of the therapeuticagent, the maximum acceptable dose in each bolus, a time interval atwhich a dose of the therapeutic agent may be delivered to a patient(lock-out interval), and so forth. Example therapeutic agents include,but are not limited to, pharmaceutical agents, insulin, pain relievingagents, anti-inflammatory agents, gene therapy agents, or the like.

Just as with the stimulation systems 10, 30 described above, for atherapy system that includes delivery of a therapeutic agent, analgorithmic model of a therapy field may be generated with the aid ofmodeling software, hardware or firmware executing on a computing device,such as programmer 20 or a separate dedicated or multifunction computingdevice. The algorithmic model of the therapy field may represent wheretherapy will propagate from the therapy system that delivers the one ormore therapeutic agents according to a particular therapy parameter set,i.e., therapy program. In some examples, the therapy field model may bebased on an anatomical data set, such as tissue density data, body fluidpressure, body fluid flow rates, body fluid diffusion rates, andeffective duration of the therapeutic agent on the target tissue. Again,the anatomical data set may be specific to the patient or may be generalto more than one patient. The anatomical data set may comprise at leastone of an anatomical image of a patient, a reference anatomical image,or an anatomical atlas.

In some cases, the algorithmic model of a therapy field resulting fromdelivery of a therapeutic agent may indicate the anatomic structures orthe tissue area that are affected by the therapeutic agent. For example,if the therapeutic agent delivers a genetic material to a target tissuesite within a patient, where the genetic material causes transgeneexpression by tissue at the stimulation site, the therapy field mayindicate the region of tissue that results in the transgene expression.The transgene expression may include an increased expression ofproteins, such as connexins, gap junctions, and ion channels, toincrease the conductivity of the tissue at the target tissue site, orthe delivered genetic material may cause expression of ametalloproteinase, an anti-inflammatory agent, or an immunosuppressantagent.

As another example, if the therapeutic agent delivers a pain relievingagent to a target tissue site within a patient, the algorithmic model ofthe therapy field may indicate the region of tissue that absorbs thepain relieving agent and/or the region of paresthesia or otherphysiological effects that may result from delivery of the therapeuticagent to the target tissue site.

The algorithm for generating an algorithmic model of a therapy fieldresulting from delivery of one or more therapeutic agents may begenerated with the aid of computer modeling techniques. The algorithmicmodel of the therapy field may indicate the diffusion of the therapeuticagent through the patient's body from a therapy delivery element. Thealgorithmic model may be an algorithmic model that is generated based ona patient anatomy, the patient's tissue characteristics, and therapeuticagent delivery parameter values. In one example, the algorithm includesequations that define drug propagation through the patient's tissuebased on the physical tissue characteristics (e.g., density) and bodyfluid flow, pressure, and diffusion characteristics adjacent the therapydelivery element. The drug propagation equations may be specific topatient 12 or may be based on information not specific to patient 12.From this information, processor 60 of programmer 20 may be able togenerate the estimated therapeutic agent propagation field that will beproduced in therapy.

In relatively static body fluids, such as like the spinal cord fluid(SCF), the drug propagation equations may define a simple diffusionmodel coupled with a model of the therapeutic agent's effective durationwithin the patient's body. Physiological parameters such a pressure atthe target tissue site may impact the diffusion rate. In relativelykinetic body fluids, such as the blood stream, the drug propagationequations may define a diffusion model that also considers the bodyfluid pressure as well as the body fluid flow rate. Generally, thesebody fluid characteristics, such as flow rate and pressure, may changerelatively quickly for a patient, e.g., based on hydration, heart rate,and the like. Accordingly, sensors may be used to regularly determinethe body fluid characteristics, and provide feedback to processor 60 (ora processor of the therapeutic agent delivery device or another device),which may then generate an algorithmic model of the diffusion of thetherapeutic agent and determine whether one or more parameter values ofthe therapeutic agent delivery are desirable based on the modeleddiffusion.

Just as with electrical stimulation therapy, therapy guidelines for atherapy system that includes therapeutic agent delivery may set forth areference therapy field that indicates a therapy field that is known toprovide efficacious therapy to manage the patient's condition, as wellas identify target anatomical structures for the delivery of thetherapeutic agent and expected therapeutic outcomes when therapy isdelivered based on the reference therapy field and/or to the identifiedtarget anatomical structures.

The techniques described in this disclosure, including those attributedto IMD 14, programmer 20, or various constituent components, may beimplemented, at least in part, in hardware, software, firmware or anycombination thereof. For example, various aspects of the techniques maybe implemented within one or more processors, including one or moremicroprocessors, DSPs, ASICs, FPGAs, or any other equivalent integratedor discrete logic circuitry, as well as any combinations of suchcomponents, embodied in programmers, such as physician or patientprogrammers, stimulators, image processing devices or other devices. Theterm “processor” or “processing circuitry” may generally refer to any ofthe foregoing logic circuitry, alone or in combination with other logiccircuitry, or any other equivalent circuitry.

Such hardware, software, firmware may be implemented within the samedevice or within separate devices to support the various operations andfunctions described in this disclosure. While the techniques describedherein are primarily described as being performed by processor 40 of IMD14 and/or processor 60 of programmer 20, any one or more parts of thetechniques described herein may be implemented by a processor of one ofIMD 14 or programmer 20, or another computing device, alone or incombination with each other.

In addition, any of the described units, modules or components may beimplemented together or separately as discrete but interoperable logicdevices. Depiction of different features as modules or units is intendedto highlight different functional aspects and does not necessarily implythat such modules or units must be realized by separate hardware orsoftware components. Rather, functionality associated with one or moremodules or units may be performed by separate hardware or softwarecomponents, or integrated within common or separate hardware or softwarecomponents.

When implemented in software, the functionality ascribed to the systems,devices and techniques described in this disclosure may be embodied asinstructions on a computer-readable medium such as RAM, ROM, NVRAM,EEPROM, FLASH memory, magnetic data storage media, optical data storagemedia, or the like. The instructions may be executed to support one ormore aspects of the functionality described in this disclosure.

The invention claimed is:
 1. A method comprising: determining, by aprocessor, a first therapy program that comprises a set of therapyparameters values; generating, by the processor, an algorithmic model ofa therapy field based on the first therapy program, the algorithmicmodel representing where therapy will propagate from a therapy systemdelivering therapy according to the first therapy program; andautomatically determining, by the processor, a second therapy programthat increases an operating efficiency of the therapy system whilesubstantially maintaining the therapy field.
 2. The method of claim 1,further comprising controlling, by the processor, the therapy system todeliver therapy to a patient according to the second therapy program. 3.The method of claim 1, wherein the algorithmic model of the therapyfield comprises a first algorithmic model of a first therapy field, themethod further comprising generating, by the processor, a secondalgorithmic model of a second therapy field representing where therapywill propagate from the therapy system based on the second therapyprogram.
 4. The method of claim 3, further comprising presenting thefirst algorithmic model of the first therapy field and the secondalgorithmic model of the second therapy field to a user.
 5. The methodof claim 1, wherein automatically determining the second therapy programcomprises automatically determining the second therapy program based onat least one of an amplitude-duration curve, a dose-response curve, astrength-duration curve, or a three-dimensional (3D) depolarizationfield model.
 6. The method of claim 5, wherein the at least oneamplitude-duration curve, dose-response curve, strength-duration curve,or 3D depolarization field model is configured based on at least one ofa patient condition, a desired therapeutic outcome, or a tissuecharacteristic of a target delivery site.
 7. The method of claim 1,wherein the second therapy program increases the operating efficiency ofthe therapy system by at least one of decreasing power consumption oroperating at an efficient amplitude determined based on a voltagemultiplier level.
 8. The method of claim 1, wherein the algorithmicmodel of the therapy field comprises a first algorithmic model of afirst therapy field, the method further comprising generating a secondalgorithmic model of a second therapy field based on the second therapyprogram, wherein substantially maintaining the therapy field comprisesmaintaining a difference between the first therapy field and the secondtherapy field below a threshold value, wherein the threshold valuedefines a maximum allowable change in at least one field characteristic.9. The method of claim 8, wherein the at least one field characteristiccomprises at least one of a centroid, a volume, an amplitude, a width ata defined amplitude, or a charge density.
 10. The method of claim 8,wherein the threshold value comprises a weighted threshold of aplurality of field characteristics.
 11. The method of claim 1, whereingenerating the algorithmic model of the therapy field comprisesrepresenting where therapy will propagate from the therapy system basedupon the first therapy program and an anatomical data set.
 12. Themethod of claim 11, wherein the anatomical data set comprises at leastone of an anatomical image of a patient, a reference anatomical image,an anatomical atlas, or a tissue conductivity data set.
 13. The methodof claim 1, wherein the therapy parameters comprise at least one of anelectrode combination, pulse width, frequency or amplitude.
 14. Themethod of claim 1, wherein the algorithmic model of the therapy fieldcomprises at least one of a two dimensional algorithmic model or a threedimensional algorithmic model.
 15. A therapy system comprising: amedical device configured to deliver a therapy to a patient according toa first therapy program that comprises a first set of therapyparameters; and a processor configured to: generate an algorithmic modelof a therapy field based on the first therapy program, wherein thealgorithmic model represents where the therapy will propagate from themedical device delivering therapy according to the first therapyprogram, and automatically determine a second therapy program thatincreases an operating efficiency of the therapy system whilesubstantially maintaining the therapy field.
 16. The therapy system ofclaim 15, wherein the medical device is configured to deliver therapyfrom the therapy system to the patient according to the second therapyprogram.
 17. The therapy system of claim 15, wherein the algorithmicmodel of the therapy field comprises a first algorithmic model of afirst therapy field, and wherein the processor is configured to generatea second algorithmic model of a second therapy field that representswhere the therapy will propagate from the therapy system based on thesecond therapy program.
 18. The therapy system of claim 17, furthercomprising a user interface that presents the first algorithmic model ofthe first therapy field and the second algorithmic model of the secondtherapy field to a user.
 19. The therapy system of claim 15, wherein theprocessor is configured to automatically determine the second therapyprogram based on at least one of at least one of an amplitude-durationcurve, a dose-response curve, a strength-duration curve, or athree-dimensional (3D) depolarization field model.
 20. The therapysystem of claim 19, wherein the at least one amplitude-duration curve,dose-response curve, strength-duration curve, or 3D depolarization fieldmodel is based on at least one of a patient condition, a desiredtherapeutic outcome, or a tissue characteristic of a target deliverysite.
 21. The therapy system of claim 15, wherein the second therapyprogram increases the operating efficiency of the therapy system by atleast one of decreasing power consumption or operating at an efficientamplitude determined based on voltage multiplier levels.
 22. The therapysystem of claim 15, wherein the algorithmic model of the therapy fieldcomprises a first algorithmic model of a first therapy field, whereinthe processor is configured to generate a second algorithmic model of asecond therapy field based on the second therapy program, and whereinsubstantially maintaining the therapy field comprises maintaining adifference between the first therapy field and the second therapy fieldbelow a threshold value, wherein the threshold value comprises a maximumallowable change in at least one field characteristic.
 23. The therapysystem of claim 22, wherein the at least one field characteristiccomprises at least one of a centroid, an area, an amplitude, a width ata defined amplitude, or a charge density.
 24. The therapy system ofclaim 22, wherein the threshold value comprises a weighted threshold ofa plurality of field characteristics.
 25. The therapy system of claim15, wherein the processor is configured to generate the algorithmicmodel of the therapy field based upon the set of therapy parameters andan anatomical data set.
 26. The therapy system of claim 15, wherein themedical device comprises the processor.
 27. The therapy system of claim15, further comprising a medical device programmer that comprises theprocessor.
 28. The therapy system of claim 15, wherein the medicaldevice is configured to deliver at least one of electrical stimulationtherapy or a therapeutic agent to the patient.
 29. A system comprising:means for determining a first therapy program that comprises a set oftherapy parameters values; means for generating an algorithmic model ofa therapy field based on the first therapy program, the algorithmicmodel representing where therapy will propagate from a therapy systemdelivering therapy according to the first therapy program; and means forautomatically determining a second therapy program that increases anoperating efficiency of the therapy system while substantiallymaintaining the therapy field.
 30. The system of claim 29, wherein themeans for automatically determining the second therapy programdetermines the second therapy program based on at least one of at leastone of an amplitude-duration curve, a dose-response curve, astrength-duration curve, or a three-dimensional (3D) depolarizationfield model.